SECTION III.
Of Disease in general.—The nature of the Plague as a Disease considered.—Of Contagion.—Whether the Plague is really Contagious or not.—Medical History of the Distemper.—Inquiry into its Immediate Causes, and whether an approaching Plague is indicated by any visible Signs.
HITHERTOwe have considered the origin of the plague entirely in a moral point of view. We have seen, that, in conformity to the general opinion of mankind, it may reasonably be supposed to have been inflicted upon mankind, the Jews particularly, for their transgressions; that, having been once introduced, it has been perpetuated, and spread from nation to nation, and that in proportion to the degree of immorality of a certain kind prevailing through the world. From this it is naturally to be inferred, that, were the human race to live at peace with one another, to disperse themselves over the face of the earth for the purpose of improving it by cultivation, and were they to be contented with what the produce of each country affords, there would be no plague among them. But we knowthat such a reformation is not to be expected, and we must take the world as we find it. The question then is, By what means shall individuals secure themselves from being destroyed by a plague which shall happen to invade any country; or how shall a person, already infected with it, be restored to health? For this purpose let us begin with considering the nature of disease in general, and of the plague particularly.
As to disease in general, physicians have differed very considerably in their definitions; and, though many have been given, few seem to be unexceptionable. That of Dr. Fordyce seems to be among the clearest and most expressive. “Disease (says he) is such an alteration in the chemical properties of the fluids or solids, or of their organization, or of the action of the moving powers, as produces an inability or difficulty of performing the functions of the whole or any part of the system, or pain, or preternatural evacuation.” But as this definition, however just, cannot be easily understood by such as are unaccustomed to medical language, I shall attempt the following explanation of the animal economy, and the diseases to which it is subject.
1. By nature our bodies are formed of certain solid and fluid parts, operating upon one another in a manner of which we know but little. Anatomists have described the structure of the human body and its parts in a certain degree, but have always found themselves lost in an inconceivable minuteness of texture. The whole structure of the human body, visible and invisible, is called itsORGANIZATION.
2. This organized body is acted upon by certain powers residing in the atmosphere, by which it becomes endowed withLIFE.
3. The operation of those powers upon a well organized body constitutes that agreeable and vigorous state which we callHEALTH.
4. The operation of any other power, substituted in place of the natural one, even upon a body perfectly organized, produces a state very different from health;commonly attended with some uneasy sensations, and which is calledDISEASE. I say it iscommonlyattended with uneasiness, but not always; for many persons within a few hours, nay, a few minutes, of their death, have imagined themselves quite recovered and well. To illustrate the meaning of what is said of the substitution of any power instead of the natural one: It is natural for man to breathe air of a certain quality; and while he does so he continues in health; but let him breathe the vapour of burning charcoal, or of fermenting liquor, mixed in considerable quantity with the air to which he has been accustomed, and he will very soon find himself diseased. Many other kinds of elastic fluids may be substituted instead of the vapour just mentioned, all of which will in a short time produce a disease in the most healthy man. The state of a diseased body being very different from that of a sound one, the appearances are consequently very different. The various appearances of disease in the human body are calledsymptomsof that disease, from a Greek word signifyingappearance.44
5. A disease proves mortal only by theDISORGANIZATIONof the body. By disorganization I mean any considerable alteration in the structure of the body, visible or invisible. The truth of this will appear from a consideration of the method by which animals may be recovered, after being to appearance dead by breathing the vapour of charcoal, or fixed air in any other form, viz. by plunging them in cold water. In a cave in Italy a continual stream of this kind of air issues from the ground. It rises but a small way, so that a man may safely enter, because his head is above the vapour; but, if he brings a small dog with him, the animal, in consequence of breathing the pernicious fluid, falls down as if dead, and would very soon die if left there. By throwing it into a lake in the neighbourhood, (cold water of any kind would answer as well) it recovers. Inthe dissection of some unfortunate people, who have been killed by breathing this pernicious fume, a manifest disorganization has been observed, viz. a rarefaction of the blood, and too great dilation, or even rupture, of the small vessels.
6. A disease cannot always be cured by removing the cause which brought it on: it is necessary also to repair the injury done to the organization. This is exemplified in the case of the dog just mentioned. Taking him out of the vapour is not sufficient for his recovery, because the organization of the body is injured; the cold water by contracting the vessels repairs the injury, and the cure is completed. To the entire preservation of this organization it is probably owing, that people have frequently recovered after being thought dead for a long time.45
7. When the organization of the body is injured, the action of the natural powers themselves occasions uneasiness, and increases the disease. The cure then is, to substitute instead of the natural power, as far as possible, the action of some other power till the organization is restored; after which the natural power must be again allowed to act, or a disease of another kind will take place. This may be exemplified in a consumption of the lungs; where, that part being very much disorganized, pure air renders the disease worse; and the sick are relieved by mixing with the common atmosphere such kinds of air or vapour as would prove pernicious to people in health. But, supposing this method to be successful, and the consumption to be entirely removed, it is plain that the use of the pure atmosphere must be resumed, or the impure air would bring on a disease in the same manner as on a healthy person.
8. The body is wasted in the natural operations of life; part of it passing off with the vapour of the breath, part by insensible perspiration, &c. Hence it naturally tends to disorganization and death, unless the waste be repaired.
9. This natural waste of the body is repaired, and health kept up, by the food and drink taken into the stomach.
10. Hence arises another set of diseases; for as the reparation of the waste, just mentioned, depends on the proper action of the stomach upon the food, and the assimilation of the latter with the substance of the body, it is plain that this operation depends both on the proper quality of the food, and the sound state of the stomach itself.
11. The body is composed of solids and fluids of different kinds, every one of which is subject to diseases peculiar to itself; but, by reason of the connexion of the parts of the body with one another, it is impossible that any one can be very much disordered without affecting all the rest. As the bond of connexion, however, is in many cases totally invisible to us, surprising instances frequently occur of one part being affected in consequence of an injury done to another very distant from it. This connexion between all parts of the body is calledSYMPATHY. Dr. Gardiner of Edinburgh, in his observations on the animal economy, &c. says, that “the stomach is the principal seat of many of the most remarkable sympathetic affections which happen in valetudinary states of the body. Every disorder accompanied with severe pain affects the stomach, whilst this viscus affects not only in its diseased state every part of the system, but at other times the effects of healthful stimuli applied to it are instantly communicated to the rest of the body, as when we take food, wine, or medicine.” Dr. Darwin in his Zoonomia informs us that the stomach is said to sympathize with almost every part of the body; but Dr. Moore, in his medical sketches, tells us that theheartpossesses a greater share of sympathy than any other part in the body, and next to it the stomach.46
12. The solid parts of the body are the bones, the muscles, brain and nerves; the fluids are, the blood, and others produced from it. The bones are known to every one; the muscles are the fleshy parts throughout the whole body; and the nerves are a kind of cords seemingly originating from the brain, and from thence accompanying the blood vessels through all parts of the body.
13. Much has been disputed about what is to be accounted the primary part of the body, on which all the rest depend; and one class of disputants have arranged themselves on the side of theblood, and the other on that of thenerves. The dispute is like one about the beginning of a circle. It cannot be decided, because the blood cannot act without nerves, nor the nerves without blood. I speak of the human body, being aware that in some animals the position may be controverted. The following is a concise state of the matter.
14. All the blood in the body passes through the heart; which has four cavities; two calledventricles, and twoauricles. These, from their position in the body, are called therightandleft. The right ventricle communicates with the right auricle, as does also the left ventricle with the left auricle; but there is no communication between the right ventricle and the left, nor between the right auricle and the left. Through these cavities all the blood passes to every part of the body, and returns from every part; but, as in the former case, we are here at a great loss where to begin its motion; for this is precisely to find the beginning of a circle. As we must begin somewhere, however, we shall do so with the right ventricle of the heart. This receives the blood returning from all parts of the body, and propels it into the right ventricle; not the whole quantity at once, for it cannot contain one half of it; but by degrees. The auricle contracts as soon as it is full; and in the time that the auricle fills, the ventricle contracts, so that it may be empty, and ready to receive the blood from the auricle. By the contraction of the right ventriclethe blood is driven into the pulmonary artery, and passes into the lungs. Here the artery branches into an infinite number of small vessels much finer than hairs; and these again, uniting into larger trunks, form at last the pulmonary vein, which brings back the blood to the heart. The pulmonary vein is inserted into the left auricle of the heart, which, as soon as it is filled with blood, contracts, and expels the blood from it into the left ventricle. From the left ventricle issues a large artery called theaorta, which by its branches supplies the whole body with the vital fluid. In all parts of the body the arteries divide themselves into innumerable small branches, which terminate in veins equally small as in the lungs; but it has been disputed whether the arteries and veins actually join each other in the form of vessels, or whether the arteries deposit the blood in small cells, from which the veins suck it up. The dispute is of no consequence, nor can it be absolutely decided, on account of the exceeding smallness of the vessels; though the microscopical observations are rather favourable to the opinion of a continuation of vessels. The veins from all parts of the body unite into larger vessels, and these again uniting with one another, form at last one very large vein called the vena cava, which opens into the right auricle of the heart, from which the circulation goes on as already described. The two ventricles of the heart, and all the veins throughout the body, are furnished with a kind of valves, which allow the blood to proceed in the way of circulation, but prevent its returning in a contrary direction.
15. The lungs, through which all the blood in the body passes, receive likewise the air which we draw in every time we breathe. They consist of two large bodies calledlobes; from their situation called the right and left. The air is conveyed into them by the wind-pipe, called also thetrachea, and theaspera arteria. On entering the cavity of the breast, the wind-pipe divides into two large branches called thebronchiæ; one of which goes to the right and the other to the left lobe of the lungs. By the further division and subdivision ofthese vessels the lungs are filled with an innumerable multitude of little tubes, terminating in exceedingly minute bladders or cells, which are the final receptacles of the air sucked in when we breathe. Each of these cells is surrounded with a kind of network of blood-vessels exceedingly small, and consisting of very thin membranes; so that, in passing through the lungs, the blood is exposed as much as possible to the action of the air.
16. It is a matter of great importance to find out what is the use of this exposure of the blood; and great disputes have taken place concerning it. In former times it was supposed that the blood received from the air avital spirit, without which it would have been totally incapable of performing its offices in the body. Later physiologists endeavoured to explode this notion. Dr. Hales particularly, by shewing that the circulation of the blood through the lungs might be continued by inflating and contracting them alternately by the fumes of burning brimstone, endeavoured to prove that the use of the air was only to give the lungs an opportunity of dilating and contracting alternately, by which means principally he thought the circulation might be carried on. This continued to be the most common hypothesis as late as the time of Dr. Huxham. It was however thought also that by the compression of the air the blood was altered in its texture, its bulk, &c. Accordingly Dr. Huxham tells us in the preface to his treatise on air and epidemic diseases, that “air fit for respiration ought neither to be too hot, nor very cold; for the use of the inspired air is to temperate the blood, which would otherwise grow too hot, and putrefy, as is evident from the experiment of the most excellent Boerhaave made in a hot house; for, if the air is more hot, or even equally hot, as the blood of any animal, it certainly soon dies.”47
17. The modern discoveries in the composition of air, have tended greatly to elucidate the use of this fluid in the lungs, and its action on the blood in respiration.Dr. Priestly first determined it to be what he terms aphlogistic process, i. e. a process by which the parts of the blood no longer proper to be retained among the rest, or at least some of them, are carried off. Thatsomethingis carried off either from the lungs themselves, or from the blood circulating through them, is evident; for the air which is taken into the lungs in a dry state, comes out of them extremely moist, and loaded with vapour. An essential change is also made in the nature of the air itself; for it now assumes in a great measure the nature of what has been called fixed air, or the fume of charcoal, or fermenting liquor, and thus becomes unfit for being breathed a second time. This change is made by the addition of some terrestrial substance to the pure atmosphere, which the latter volatilizes and carries along with it.48
18. But, whatever may becarried offfrom the blood, during its passage through the lungs, something is certainlyaddedto it, for the blood in the pulmonary artery is of a dark red, but when it has undergone the action of the air in the lungs, and returns by the pulmonary vein, it is then of a bright scarlet, which colour it retains through all the arteries of the body, but loses it on its return through the veins. This scarlet colour is communicated to blood in all cases when exposed to the air; and Dr. Priestley has observed that it is acted upon by the air even through a bladder; much more then must it be so through those very thin membranes which form the coats of the fine pulmonary vessels. What this subtile matter is which the blood receives, shall be afterwards inquired into; at present it is sufficient to take notice that it is absolutely necessary, for the purposes of life, that the blood should pass through the lungs: for, as Dr. Huxham observes, “we see neither nutrition, nor the motion of the muscles, performedby any blood that hath not passed through the lungs; this is observable from the coronaryarteries49to the ultimate ramifications of the aorta.” As the previous circulation of the blood through the lungs therefore is absolutely necessary to the growth and life of the body, and as the blood certainly receivessomethingfrom the air, we must account this a proof, and no inconsiderable one, that the air contains avital spirit, which it imparts to the blood in the lungs. But, before we proceed farther on this subject, it is proper to take some notice of
19.The nerves.These, which constitute such a remarkable and important part of the human body, are white cords, of a soft pulpy substance, defended by a tough skin which goes along with them as far as they can be traced. All the nerves either originate from the brain, or terminate in it. The former doctrine hath been generally adopted, and in conformity to that doctrine the following account of the nerves is laid down. The brain is enclosed in the cavity of the scull, but not without the intervention of two membranes, called theduraandpia mater, to prevent injury from the hard bones, as well as for other purposes. The brain is divided into two lobes, the right and left. It is composed of two different kinds of substance, the outermost called the cortical, the innermost the medullary substance; the latter seems composed of fine fibres. The whole of the medullary part of the brain terminates in a substance called thecerebellum, very much resembling the brain, but smaller. The cerebellum terminates in another substance resembling the medullary part of the brain, called themedulla oblongata. The cerebellum lies in the back part of the head, and the medulla oblongata under it. The latter terminates in the spinal marrow, extending from the lower and back part of the head to the lower extremity of the back bone, and is enclosed in the hollow of that bone. The nerves proceed from these four substances, viz. the brain, the cerebellum, the medulla oblongata, and spinal marrow. As they pass to allparts of the body they accompany the arteries, dividing with them into innumerable small branches; but they do not return with the veins; so that they seem not to contain any fluid which goes and comes, or which circulates like the blood. The nervous fluid, if any such there be, seems to move constantly one way, either to the brain or from it.
20. Hitherto we have noticed only things which are evident to our senses, and which the industry of anatomists has abundantly evinced; but now our subject renders it necessary to step aside a little into the obscure regions of theory and conjecture. The muscles, as we have formerly said, are the fleshy parts of the body; and by them all the motions of the body are performed. The flesh is distributed into distinct portions, each of which is enclosed in a membrane belonging to itself. Each of these portions is a muscle, and each muscle has a branch of an artery and the branch of a nerve belonging to it. On both these the action of the muscle depends; for, if we cut the nerve belonging to a muscle, it immediately loses all power of action; and if we cut the artery which accompanies the nerve, it does the same. As therefore the blood is found to receivesomethingfrom the air, and as it loses this when passing through the arteries, and as the nerves lose their power when the communication with the blood is cut off, it seems extremely probable, that what is imbibed by the blood in the lungs is taken up by the fine ramifications of the nerves, and is no other than the immediate principle of life and sensation. Thus we will establish a doctrine directly opposite to that commonly received; for, instead of supposing that the nerves originate from the brain, we are now led to suppose that they terminate in it. Instead of supposing that the sensations originate in the brain, we will be led to suppose that every sensation originates in the organ appointed for that sensation. Thus we are conscious that oureyes, not ourbrain, are the parts of our body which immediately perceive the light; our fingers, or any other parts of the body,feelwhat is applied to them; and of consequence we havereason to believe that theanimal spirits,nervous fluid, or whatever we please to call it, proceed from the surface of the body inwards to the brain, not outwards from the brain to the surface of the body. The brain itself seems to resemble a large collection or reservoir of water, in which the sensations, like so many small streams from every part of the body, unite, and in which our intellectual faculties reside in a manner totally inexplicable by us. Thus far it seemed necessary to theorise, in order to form some idea, however obscured, of the connexion between the nerves and our sensitive and intellectual, or, if we please to call them so, ourspiritualfaculties.
21. In consequence of this very intimate connexion between the blood and nerves, it is easy to see that any injury done to the one may very greatly affect the other; and that a very slight, nay, to us imperceptible, change in the organization of either, may produce the most grievous, and even incurable disorders throughout the whole body, or in any particular organ. Let us now consider a little farther the blood-vessels.
22. It hath been a question, whether in the structure of these vessels nature hath observed an exact proportion. For instance, if the blood passes by a kind of starts through four cavities, as we are assured that it does, it seems natural to suppose that these four should be exactly equal. This, however, hath been denied; and some, from its accommodating the human frame to their theory, have fancied that they saw the use of such disproportionate work. Dr. Huxham expresses himself in the following words: “Nor doth the air only refrigerate the blood, but, by preventing its too great ebullition, and condensing it, hinders it from bursting the vessels. This indeed is of exceeding great importance, if, with the very learnedHelvetius, we suppose the capacity of the right ventricle of the heart to be greater than that of the left, and that the pulmonary arteries are larger than the correspondent veins; for it thence follows, that the blood ought to be considerably condensed by the inspired air, that an equal quantity of blood may be received, in one and the same time, bythe pulmonary veins and left ventricle of the heart, that is thrown off from the right ventricle, and through the more capacious pulmonary arteries. This indeed many deny, asserting quite the contrary. It is necessary, however, that the aorta should receive as much blood from the left ventricle of the heart, as is thrown off from the right ventricle through the pulmonary artery; and that in the very same and equal time, or a fatal deluge would soon overwhelm the lungs, because the contraction of each ventricle is made at one and the same time; we always find therefore the aorta and pulmonary artery, in a natural state, equal on this account; also the capacity of the ventricles ought to be equal, that they may receive, in one and the same space of time, equal quantities of blood,” &c.
If any thing farther is necessary upon this subject, we may still observe, that if the blood were at all condensed by the air, it would be so unequally, because the air is at some times much colder than at others; and thus the disproportion of the cavities of the heart to one another could not fail of producing the most disagreeable if not fatal effects. We often see what terrible consequences ensue upon the enlargement of any part of an artery near the heart; and these would, sometimes at least, be felt by every individual.50
It is true, indeed, that this objection will in some degree hold, even though we suppose all the cavities of theheart to be equal, and the capacities of the blood vessels to be perfectly uniform throughout the whole body. For, if we suppose the blood to be at all condensed in the lungs by the coldness of the atmosphere, it must undoubtedly follow, that while passing from them it occupies less space than before it arrives at them. Hence the pulmonary vein, the left auricle of the heart, the left ventricle, the aorta, and all the rest of the arteries for a considerable way, must be comparatively empty, even though they receive as much fluid as fills the vena cava, right auricle and ventricle of the heart, and pulmonary artery. The equality which ought to prevail in the system, and which indeed cannot be dispensed with, can only take place in those remoter branches of the arteries in which the blood has reassumed its former state of dilation or rarefaction.
23. If we consider this matter attentively, we shall find it not a little mysterious. Every time we breathe out the air we have sucked into our lungs, a considerable quantity of moist vapour is breathed out along with it; but it has been proved by undeniable experiments that the emission of aqueous vapour from any substance cools it in proportion to the quantity of vapour emitted. Every breath we draw, then, cools the lungs, and consequently the blood, to a certain degree, and, as the number of times that we breathe in a day is exceedingly great, the cold produced by the evaporation ought to be in proportion. But we see that, notwithstanding all this cooling, whether we breathe cold air or hot air, the temperature of the body remains still the same. The air then, though constantly carrying off the heat of the body, does not cool it in the least by its action on the lungs. The only possible way of solving this apparent contradiction is, by supposing that the air, when acting upon the blood in the lungs, leaves precisely as much heat as it carries off, and therefore, though we breathe ever so long, we cannot by this means become either hotter or colder.
24. To illustrate this subject, we might now enter into an inquiry concerning the origin and cause ofanimal heat; but this will be touched upon hereafter. We shall here only take notice that the heat of the body is almost universally allowed to proceed from the lungs. It has likewise been demonstrated, that the air does in fact contain an incredible quantity of heat, even when it appears to us to be extremely cold. A certain proportion of this heat is separated from it every time we breathe; and if, either by the mixture of other fluids with the air we breathe, or by any change in the organization of the body itself, a greater or smaller proportion of heat should be communicated to the blood, disease must ensue.
25. To sum up then what has been said concerning the blood and nerves: The whole mass of fluid passes from the right side of the heart to the lungs. In the lungs it receives from the airsomething52necessary to the functions of life and sensation, and purifies itself from those matters which might prove pernicious. From the lungs it passes to the left side of the heart, and thence through the whole body. In its passage through the body, it is accompanied with nerves, which, taking up from the arterial blood thatvital spiritreceived from the air, convey it to all the organs of motion, of sensation, and to the brain, where the whole powers of perception being united form ourintellectual faculties, and, as far as our senses can perceive, the human spirit itself. The blood, thus deprived of its spirit, is collected from all parts of the body by the veins, and returned to the right side of the heart, from whence it is again sent to the lungs, and the process carried on as before. This hypothesis concerning the peculiar function of the nerves I first inserted in theEncyclopædia Britannica, second edition, under the articleBlood, in the year 1778. It has been since continued in the third Scots edition, and from thence into the Irish and American editions.
26. It has already been observed, that the body is subjected to a continual waste. One source of thiswaste is the breath, by which a considerable part passes off in vapour. A great quantity also passes off by the pores of the skin; frequently in a perceptible liquid calledsweat, but oftener in an invisible vapour from all parts of the body, calledinsensible perspiration. The latter has been thought to be the great source of waste to the human body; and it is certain, that if any person in health be weighed when he rises in the morning, he will be found considerably lighter than when he went to bed. The loss of weight in this case proceeds not only from the pores of the skin, but from the lungs; but though physicians have made a general allowance for both these, I have not heard of any experiment by which we can determine how much passes off by the one, and how much by the other, nor indeed does it appear easy to make such an experiment. Galen plainly overlooks the perspiration from the lungs entirely. “This excrementitious vapour (says he) is expelled through small orifices, which the Greeks call pores, dispersed all over the body, and especially over the skin, partly by sweat, and partly by insensible perspiration, which escapes the sight, and is known to few.” Sanctorius, and the succeeding writers, have classed both together indiscriminately; allowing the discharge to be so great, that if eight pounds of aliment be taken in, five of them pass off in this manner. In a system of anatomy, published at Edinburgh in 1791, the author says, that the discharge by the skin “is even much larger than this (the discharge from the lungs we may suppose) since it not only throws off a quantity of the aliment, but likewise what is added to the blood by inhalation, which, entering often in a very considerable quantity, is thus again expelled.” The same author likewise says, that the “perspirable matter from the skin is principally water,” and that it issues in such quantity as to be seen in subterraneous caverns evidently flying off from the surface of the body like a dense vapour. But other physiologists, particularly Dr. Blumenbach, inform us, that the matter of insensible perspiration is quite similar to the discharge from the lungs, particularly containinga great quantity of fixed air. The same account is given in Chaptal’s chemistry, on the authority of Messrs. Milly and Fouquet. This may be looked upon as a valuable discovery, especially in conjunction with that related by Drs. Beddoes and Girtanner, viz. that the flesh of animals contains a quantity of oxygen. Dr. Girtanner obtained a quantity of this air from the raw flesh of animals, and says that it may be repeatedly obtained by exposing the flesh to the atmosphere, and distilling with a heat of 60 or 70 degrees of Reaumur’s thermometer (something below that of boiling water.) Hence it is natural to conclude, that, as the discharge from the lungs purifies the blood from its useless parts, so does the insensible discharge from the skin purify the solid parts from those particles which are no longer useful. The probability of this also becomes greater by considering, that in diseases, when the quantity of matter to be thrown off is very great, the skin becomes foul, the teeth furred with black sordes, &c. all which disappear as soon as the quantity of the offensive particles is reduced to its natural standard. As to any considerable quantity of aqueous vapour being discharged this way, unless in case of sweat, it does not seem probable; for in such a case our clothes would always be moist; and in the night time the accumulation of moisture would certainly be perceptible. The sweat is entirely of a different nature from the insensible perspiration, and blood and evensandhas been known to issue through the skin along with it. (See the Anatomical System above quoted.)
27. This very considerable waste of the body is repaired by the aliment taken into the stomach. In the mouth it is mixed with a considerable quantity of the liquid calledsaliva, and in the stomach with another called thegastric juice, with which that organ always abounds. From the stomach it passes into the intestines, where it is mixed with other two fluids; one called thepancreatic juice, the other thebile. This last is of a yellow colour, and is sometimes produced in enormous quantities, insomuch that Dr. Wade, in his account of the fevers in Bengal, mentions some patients whohave voided by stool half a gallon of bilious matter in one day.
28. In the stomach principally the aliment undergoes a certain change calleddigestion, by which it becomes capable of being converted into the substance of the body. Much has been inquired and disputed, to no purpose, about the nature of this change, and how it is effected. One party has declared forattrition; a second forputrefaction; a third forheat; a fourth have supposed that our meat was digested bychewing; as if, like the lobster, people had teeth in their stomach! and, lastly, some learned moderns, after much pains and trouble, have found out that it is digested bysolution. Dr. Moore has summed up the discoveries concerning digestion in the following words: “The food, being previously divided and blended with the saliva and air by mastication, (chewing) is swallowed, and meets in the stomach with the gastric juice, whose dissolving power, assisted by the natural heat of the place, is the principal agent in digestion. The process is completed by the pancreatic juice and bile, the nutritious parts of the food being by this process converted into chyle for the support of the body, and the grosser parts thrown out.”53
29. The inside of the stomach and intestines are full of the mouths of innumerable small vessels, which continually suck up from the aliment, as it passes downwards, the finer parts, in form of a white liquid, calledchyle; and from the whiteness of their colour the vessels have the name oflacteals, from the Latin wordlac, milk. After passing through the substance of the stomach and intestines, and running along the membrane called themesentery, to which the intestines are attached, the lacteals unite in a large reservoir called thethoracic duct; and this again opens into a large vein on the left side, called thesubclavian, which conveys the blood from half the upper part of the body; soon after terminating in the vena cava, by which the chyle is conveyed to the heart, thence to the lungs, and so on in the commoncourse of circulation. The conversion of the chyle into blood is called the process ofsanguification.
30. The blood, thus formed out of the aliment we swallow, is not one uniform fluid like water, but composed of three distinct substances; one, which gives it the red colour, and seems to be composed of little round globules; another, quite colourless, but of a viscid nature, and which very soon coagulates, called thelymph; and a third, of a yellowish colour, and retaining its fluidity much longer, called theserum. A remarkable property of this last fluid is, that air can act through it upon the blood; for Dr. Priestly found that a portion of black blood assumed a bright, florid colour from the air, even though covered with serum an inch deep. When blood is drawn, the red globules are detained by the lymph which coagulates, and both together form the red mass calledcrassamentum; the serum remaining fluid, and retaining its name.
31. Besides these fluids, the blood either invisibly contains, or is capable of being converted into, a great many others; for all the fluids in the body are separated from it, and all of them, the bile only excepted, from the arterial blood, before it has lost that portion of its spirit which it imbibes from the air. When a fluid is to be secreted, sometimes it is done only by an infinity of small vessels branching off from the arteries, and depositing the liquids which pass through them in particular places; and such are the fluids which moisten the inside of the body, and which are carried off by the breath, or by sweat. But this separation does not by any means hinder the artery from terminating in its usual way in a vein, for in no case is the whole substance of the blood converted into any other liquid; all of them appear to be contained in it. But the greatest number of fluids are separated by means of certain substances calledglands. These are small round or oval shaped bodies; each of them enclosed in a membrane or skin which separates it from the other parts, and each furnished with a small tube called theexcretory duct, through which the liquor separated in the gland passes to itsplace of destination. Each gland has also an artery and nerve, and a vein to bring back the blood after it has parted with the fluid intended to be separated. The bile is separated in the liver from the blood of a large vein called thevena portarum, formed by the union of some of the veins of the intestines and mesentery. This vein branches out through the liver like an artery, terminating in other veins, which at last bring back the blood to the heart.
32. As the human body is thus furnished with an apparatus for separating and carrying off, it is also furnished with one for absorbing or taking in. All the inward parts of the body are moist; and the moisture is furnished by the small vessels above described, and which separate part of the lymph from the blood. By such continual separation the cavities of the belly, breast, brain, &c. would soon be filled with liquid, were not some means provided for carrying it off as fast as it is formed. The means in question are a set of small vessels calledlymphatics. These “arise from the internal surface of the breast, belly, and every cavity of the body; they also overspread the whole external surface of the body, and large lymphatic vessels are usually found close to the large blood vessels of the extremities, besides those small superficial ones which lie above the muscles in the cellular membrane (the fat or rather the membrane containing it.) The large viscera generally have two sets of lymphatics, one lying on the surface of the viscus, and the other accompanying the blood vessels belonging to it. The faculty of absorption, though refused to the lymphatics, was ascribed by many anatomists to common veins, and this opinion continued to prevail in some degree, until Hunter and Monro totally overturned it, exploding at the same time the notion that any of the lymphatics are continuations of arteries, and establishing, beyond a doubt, that all are absorbent vessels.”54All the lymphatics terminate in the thoracic duct; so that the liquid separated by theexhalant arteries(so thevessels are termed by which that fluid is separated) is again mixed with the blood, and again performs the same offices.
We have now taken a review of the several parts of the human body, slight and superficial indeed, but such as the limits of this work would allow, and sufficient to furnish to those entirely unacquainted with medical matters some general ideas on the subject. We have seen that the body, in general, consists principally of four great parts, the blood-vessels, the lymphatic vessels, the nerves, and the muscles. Besides these we enumerate the glands and membranes; the former being nearly allied to the blood-vessels, the latterapparentlyto the nerves. The bones, having no concern with our present inquiry, are not taken notice of. The stomach and intestines, being principally composed of muscular fibres, nerves, and blood-vessels, must be considered as belonging to these departments. Each of these large divisions has obtained the name ofsystem; and even the subdivision of the blood-vessels into arteries and veins. Thus the arteries of the body, taken collectively, are called thearterial system; the veins thevenous system; the brain and nerves thenervous system; the muscles themuscular system; the lymphatics thelymphatic system; and the glands theglandular system; &c. These appellations have been given for the sake of distinctness and perspicuity, but they have had a bad tendency. Insignificant disputes have arisen concerning the superiority of one system to the other, and which is to be accounted theprimum mobileof the body. By observing also thegeneralstructure of the body in a more full and ample manner than that of the parts which compose it, physicians have been apt to generalize too much in their theories, and to fancy that from a few obvious laws they might be able to explain the phenomena of disease in almost every possible variety. To illustrate this, let us take the blood for an example. This to sight appears an homogeneous fluid; and Boerhaave and others have ascribed diseases to some defect or bad quality of the blood. But this fluid consists of three parts, each, as far as we can perceive, essentially distinct from the other;viz. the lymph, serum, and red globules. As each of these happens to be diseased, the cure must be different; or if two happen to be diseased, the medicines must still be varied. But, besides these general diseases arising from what, like the blood, is common to the whole body, each component part of the body has an arterial system, a venous system, a nervous and lymphatic system, &c. belonging to itself; all of which, though dependent on the body at large, have yet laws of their own, in consequence of which any one of them may be considerably diseased without much affecting the general system; and this constitutes what is calledlocaldisease. Again: The parts of the body are so connected with one another, that the disease of one may show itself in another; or it may affect the whole body in such a manner as to produce a general disease; though Dr. Rush considers this last, at least from injuries of the viscera, as a rare occurrence;55but we certainly know that general diseases are very often followed by evident diseases of particular organs; and in these cases it is impossible to say whether the general disease did not begin, though imperceptible to us, in that very organ in which we suppose it to terminate when the local disease was come to such an height as to be evident to our senses. In some cases it is plain that local injuries will bring on most violent diseases of the whole system. Thus a local inflammation of the end of one of the fingers, by physicians called aparonychia, has been known to induce a most violent fever, nay, even to occasion death. These violent symptoms end as soon as the suppuration is completed; so that, were it not for the excessive pain of the inflammation, we might be apt to suppose that the fever terminated in the suppuration, whereas it evidently was occasioned by the local disease, or the tendency of the part to suppurate; the pain and inflammation being necessary preliminaries. Again: When an intermittent fever is said to terminate, or to be followed, by a hardness of the liver, we do not certainly know whether an original disease of the liver might nothave been the cause of the intermittent. From a consideration of all these things, viz. the extreme diversity of parts which compose the human body, the ultimate invisibility of the structure of each, the incomprehensible manner in which they are united, the equally incomprehensible dependence they have upon one another in some cases, and independence in others, the numerous laws by which they are governed, and which must be very much unknown to us, the invisible and incomprehensible nature of the powers which act upon them, &c. &c. I say, when we consider all these things, the boldest theorist must be humbled when he attempts to account for the phenomena of disease in any one instance. The excessive difficulty in which we are involved is beautifully described by Dr. Ferriar when speaking of hysterics; and obstacles equally insuperable by our theories will undoubtedly be met with in any other distemper. “We are ignorant (says he) by what laws the body possesses a power of representing the most hazardous disorders, without incurring danger; of counterfeiting the greatest derangement in the circulating system, without materially altering its movements; of producing madness, conscious of its extravagances; and of increasing the acuteness of sensation by oppressing the common sensorium. In hysterical affections all these appearances are excited, which are incompatible with the reasonings of every system-maker who has yet endeavoured to explain the inexplicable. Nature, as if in ridicule of the attempts to unmask her, has, in this class of diseases, reconciled contradictions, and realized improbabilities, with a mysterious versatility, which inspires the true philosopher with diffidence, and reduces the systematic to despair.”
Notwithstanding all these difficulties, however, physicians have theorised, and that with such animosity, as if all the arcana of nature had been laid open to every professor who thought proper to invent or new-model a system; though the constant succession of theories might certainly have shown them the vanity of such attempts. Some of these we must now consider.
Medical theorists have exerted their greatest abilities in explaining the nature of those general diseases affecting the whole body, denominatedfevers; and which are likewise calledacutediseases, from the violence with which they sometimes attack, and the rapidity with which they run through their course. Dr. Fordyce says, that fever will sometimes kill infive minutesfrom the first sensation of uneasiness. Ancient physicians have described a number of fevers, which they supposed to be of different species, and accordingly have distinguished by different names. Modern system-makers have added to the number; so that a bare detail of the names which they have given to their divisions and subdivisions, would constitute a very formidable catalogue; but the latest practitioners are decidedly of opinion that there is but one kind of fever, varying itself according to circumstances. Dr. Rush declares himself of this opinion in the most express and positive terms. “There is (says he) but one fever. However different the predisposing, remote or exciting causes may be, . . . still, I repeat, there can be but one fever. . . . Thus fire is an unit, whether it be produced by friction, percussion, electricity, fermentation, or by a piece of wood or coal in a state of inflammation.”56
“I have said that there is but one fever. Of course I do not admit of its artificial division into genera and species; a disease which so frequently changes its form and place, should never have been designated, like plants and animals, by unchangeable characters. . . . Much mischief has been done by nosological arrangements of diseases. They erect imaginary boundaries between things which are of an homogeneous nature. . . . They gratify indolence in a physician, by fixing his attention upon the name of a disease, and thereby leading him to neglect the varying state of the system, &c.”57
So much then having been said and written upon the disease in question, one might be apt to suppose that thenature of fever would have been thoroughly investigated, and its causes explained in the most satisfactory manner, long before this time. Instead of this, however, we find it still like a word which every body uses, and nobody understands. Dr. Fordyce, who has lately written a treatise on the subject, endeavours to prove that there is not any single symptom from the existence of which we can certainly determine the presence of this disease. “Fever (says he) has obtained its name in Greek, Latin, Arabic and Persian, principally from the idea of heat:pur, in Greek fire;febrisin Latin, fromfervere, to burn,” &c. This idea, he goes on to demonstrate, is erroneous; as the body of a feverish patient frequently sinks the thermometer below the natural standard; while the patient sometimes finds himself cold when the thermometer shows him to be really hot, and hot while the same instrument shows him to be cold. Neither is cold, followed by heat, a certain indication of the presence of fever, as many fevers begin without any previous sensation of cold. Frequency of the pulse also is no certain sign; and having discussed this last symptom he concludes thus. “If we examine the restlessness, anxiety, state of the tongue, head-ach, or any other of the symptoms which often take place in fever, we shall find that they also may be present when there is no fever, and absent in a patient afflicted with this disease; and therefore we cannot allow that there is any pathognomic symptom of fever.”58Dr. Rush declines giving any definition of fever;59but, with all due deference to these two very experienced physicians, we must account such extreme scepticism altogether erroneous. If fever cannot be defined, it cannot be described; for adefinitionis no other than a shortdescription. If again there be no single symptom by which the presence of fever can be known, it is impossible that there can be anycombinationby which it can be known, any more than we can form an unit by any combination of cyphers. In fact Dr. Fordyce himself is at last obliged to acknowledgethat there is a certain symptom with which fevergenerallybegins; and, by his insisting upon it in various parts of the work, we must certainly be induced to suppose that it was by this sign principally that he determined whether his patients had a fever or not. “The first appearance (says he) which generally takes place is uneasiness and restlessness; a general uneasiness, the patient feeling himself ill, but incapable of fixing on any particular part of the body. This uneasiness affects the mind at the same time. Perhaps in this case it is the mind that is first affected. . . . Along with this uneasiness there is a restlessness, the patient wishing to change his place or posture frequently; the mind cannot likewise rest upon one object; it often wanders from one to another subject. At the same time there is a feel of weariness which resists the disposition in the patient to change his place and posture, and resists the disposition of the mind to alter the object of its attention, rendering the wish for such changes ineffectual. With these arises an actual inability of exerting the muscular powers, or performing any of the functions of the body; and also an actual inability of exercising the great faculties of the mind, the powers of perception, memory, arrangement of ideas, and of the judgment, in the same degree that they existed in health. The degree in which these take place is extremely different in the attacks of different fevers; but these appearances arevery rarelyabsent, although indeed they may also happen in other diseases.”
Dr. Rush accounts the lassitude with which fever begins, one of the transient phenomena of it; and this with other phenomena he callssymptoms. Such as are more permanent and fixed, and which by other writers have been reckoned different species, he callsstates; and of these he enumerates forty. Such as have any relation to the plague are as follow.
I. TheMALIGNANTstate, known by attacking frequently without a chilly fit, is attended with coma, a depressed, slow or intermitting pulse, and sometimes by a natural temperature or coldness of the skin. . . .This depressed state of fever more frequently when left to itself terminates in petechiæ, buboes, carbuncles, abscesses and mortifications, according as the serum, lymph, or red blood, is effused in the viscera or external parts of the body.
2. TheSYNOCHA, or common inflammatory state; attacking suddenly with chills, succeeded by a quick, frequent and tense pulse, great heat, thirst, and pains in the bones, joints, breast or sides.
3. TheBILIOUSstate of fever; known by a full, quick and tense pulse, or by a quick, full and round pulse without tension, and by a discharge of green, dark coloured or black bile from the stomach and bowels. This state sometimes assumes the form of an hectic; the patient feels no pain in his head, has a tolerable appetite, and is even able to sit up and do business.
4. TheTYPHUSstate; known by a weak and frequent pulse, a disposition to sleep, a torpor of the alimentary canal, tremors of the hands, a dry tongue, and, in some instances, a diarrhœa. Sometimes it assumes symptoms of synocha on the eleventh, fourteenth, and even twentieth days. The common name of this state is thenervousfever.
5. Intermissions, or theINTERMITTINGandREMITTINGstates, occur most distinctly and universally in those which partake of the bilious diathesis.
6. TheSWEATINGstate occurs not only in the plague, but in the yellow fever, small pox, pleurisy, rheumatism, hectic and intermitting states.
7. TheFAINTINGstate; occurring in the plague, yellow fever, small pox, and some states of pleurisy.
8. TheBURNINGstate. This is attended not only with an intolerable sensation of heat in the bowels, but with a burning sensation excited in those who touch the patient’s skin. It occurs mostly in the remitting fevers of Asia.
9. TheCHILLYstate differs from a common chilly fit by continuing four or five days, and to such a degree that the patient frequently cannot bear his arms out of bed. The coldness is most obstinate in the hands andfeet. A coolness only of the skin attends in some cases, which is frequently mistaken for an absence of fever.
10. TheINTESTINALstate; including the cholera morbus, diarrhœa, and cholic.
11, 12, 13, 14, 15. TheAPOPLECTIC,PHRENETIC,PARALYTIC,LETHARGICandVERTIGINOUSstates.
16. TheERUPTIVEstate; including the small pox, measles, and other exanthemata of Dr. Cullen.
17. TheHÆMORRHAGICstate; known by fluxes of blood from various parts of the body.
18. TheCONVULSIVEorSPASMODICstate. Convulsions are frequently attendant on the malignant state of fever.
19. TheCUTANEOUSstate; attended with various eruptions on the skin, particularlypetechiæ.
These include the most remarkable varieties described by physicians as different species. From the subsequent account of the symptoms of the plague, it will appear that this single distemper monopolises, as it were, the symptoms, at least the most dangerous and terrible, belonging to them all. Those nosologists therefore who suppose the states of fever above described to be different species, instead of saying that the plague belongs to one kind of fever, ought to say that it is a complication of a great many different kinds. But here a question arises: Do all the varieties of fever just now described, or do all the other fevers described by different authors, include all the different modes by which the plague makes its attack? If so, then we know that the plague really partakes of the nature of fever, or may be accounted the highest degree of it. This is the opinion of Dr. Rush; for in his 4th vol. p. 153, he considers the different inflammatory states of fever, according to their strength, in the following order. 1. The plague. 2. The yellow fever. 3. The natural small pox. 4. The malignant sore throat, &c. To this I can have but one objection, and to me it appears insuperable; viz. that the plague frequently destroys without any symptom of fever; and, if so, we must certainly account it a distemper of another kind. To decide thismatter, let us compare the symptoms of the most violent fever with what happens in times of violent pestilence. We can scarce imagine a fever more powerful than that which destroys in five minutes, and the following is the description of it from Dr. Fordyce. “When the first attack of fever has been fatal, it has been classed among sudden deaths, and all of these have been very erroneously called apoplexy, or syncopy (fainting.). . . . When the attack is fatal, it sometimes kills in five minutes, sometimes it requires half an hour, seldom longer than that time. While the patient is yet sensible, violent head-ach with a great sense of a chilliness takes place, the extremities become very cold, and perfectly insensible; there is great prostration of strength, so that the patient is incapable of supporting himself in an erect posture; he becomes pale, his skin is of a dirty brown, and he is soon insensible to external objects; the eyes are half-open, and the cornea somewhat contracted. If the patient goes off very soon, the pulse is diminished, and at last lost, without any frequency taking place, but if it be longer before he dies, the pulse becomes excessively small and frequent; all the appearances of life gradually subside, and the patient is carried off. Of this the author has seen instances, sometimes at the first attack, oftener in the returns of the disease, although very few.”
This no doubt is very terrible, and no plague whatever can exceed it. Indeed, whendeathis the termination, it signifies little what thediseaseis called. But the question is not whether fever or plague is the most dreadful, but whether they are the same. Now, from the above description, it is plain that fever never kills without some warning. In the present instance, head-ach and chilliness give a certain, though short, warning of the ensuing catastrophe; but, in violent plagues, Dr. Sydenham informs us, that people have been suddenly destroyed as if by lightning. Dr. Guthrie assures us that in the last plague at Moscow he has seen soldiers drop down suddenly as if they had been struck by lightning, or by a musket ball; yet some of these recoveredby bleeding and proper management; but it is certainly not unreasonable to suppose that many, who were not thus taken care of, perished. Dr. Hodges speaks of the contagion of the plague in the most energetic terms. He says, “it is so rare, subtile, volatile and fine, that it insinuates into, and resides in, the very pores and interstices of the aerial particles. It is said to be of a poisonous nature also, from its similitude to the nature of a poison, so that they seem to differ in degree only; for the deadly quality of a pestilence vastly exceeds either the arsenical minerals, the most poisonous animals or insects, or the killing vegetables; nay, the pestilence seems to be a composition of all the other poisons together, as well as in its fatal efficacies to excel them. . . . The contagion of the plague is more active than lightning, and in the twinkling of an eye carries to a distance putrefaction, mortification and death. As for the manner whereby it kills, its approaches are generally so secret, that persons seized with it seem to be fallen into an ambuscade or a snare, of which there seems to be no suspicion. . . . In the plague of 1665, as in many others, people frequently died without any symptoms of horror, thirst, or concomitant fever. A woman, who was the only one left alive of a family, and in her own opinion in perfect health, perceived upon her breast the pestilential spots, which she looked upon to be the fataltokens; and in a very short space died, without feeling any other disorder, or forerunner of death. . . . A youth of a good constitution, after he had found himself suddenly marked with the tokens, believed at first that they were not the genuine marks, because he found himself so well; yet he was dead in less than four hours, as his physician had prognosticated. A fever, however, did for the most part show itself, and was always of the worst kind. Sometimes it seemed to resemble a quoridian, sometimes a tertian; there never was a total cessation, but every exacerbation was worse than before.” In like manner the author of the Journal of the Plague Year informs us that many, supposingthemselves, and supposed by others, to be in good health, would suddenly find themselves seized with great sickness, crawl to a bench, and instantly expire. “Many (says Dr. Hodges) in the middle of their employ, with their friends and other engagements, would suddenly fall into profound, and often deadly sleeps.”
It is needless to multiply examples: the above are sufficient to show that the plague, when in its most violent state, kills suddenly and imperceptibly, and that like the bite of a vampire,60without producing any sensible disorder. In a state somewhat inferior, it excites the most malignant fevers; in one still inferior it produces fevers of a milder nature, and so on until we find it so mild, that those infected with it are not even confined to their bed. In all this inquiry, however, we find the secrecy and invisibility of the pestilence, so often mentioned in scripture, still confirmed. Other distempers may “waste openly at noon-day,” but this always “walks in darkness.”
In one of the inferior stages of this distemper the body is affected with those eruptions named buboes and carbuncles. Dr. Patrick Russel, in his treatise on the plague at Aleppo, divides the symptoms of the distemper into six classes. In the first there were no eruptions, and all the patients of this class died. In the second, and all the rest, there were buboes and carbuncles. But, in the latter of these especially, it is worthy of remark,that they appear neither as a suppuration, nor as a common mortification, but like the eschar formed by a caustic, which can scarcely be cut by a knife. This appearance is not to be met with in any other disease. In many there are mortifications of various parts of the body, but all these are soft, and seemingly corruptions of the flesh. When a person dies of any ordinary distemper, the flesh soon corrupts and dissolves, but there is no example of its turning to a hard eschar like that made by a hot iron, or the caustic with which issues are made. This shews not merely a cessation of life, but the operation of some very active power in the body, like fire, tending to destroy the texture of it entirely, and to reduce it to a cinder. This power seems also to operate internally in the fleshy parts; for when the bodies of those were opened who died with thetokens, as they are called by Dr. Hodges, upon them, the mortification was always found much larger inwardly than it appeared to be on the outside. The tokens themselves are by Dr. Hodges called “minute distinctbiasts, which had their origin from within, and rose up in little pyramidal protuberances, sometimes as small as pins’ heads, at others as large as a silver penny; having the pestilential poison chiefly collected at their bases,” &c.
That the plague was by the ancients reckoned a disease of a nature different from all others, appears from Galen, as quoted by Deusingius. “What is called thepestilenceis most properly remarked by Galen not to be agenusof any known disease. For whatever diseases and symptoms are associated with the plague, truly and properly so called, the same are wont to be calledpestilentialdiseases; of which indeed there are an innumerable multitude, and these not always nor every where the same.”61
In like manner Diemerbroeck, as quoted by Allen, gives his opinion, that “The plague is something differentfrom a fever, and a fever is only a symptom of it, as I havevery oftenobserved; and therefore some very ill define the plague by a fever, since a fever does not essentially belong to it. . . . A pestilential fever, thecompanion of the plague, is not occasioned by a pestilential venom, but by the mediation of putrefaction; that is, it is not produced because the humours are infected with the pestilent venom, but because the heart, being irritated, overwhelmed and much weakened by the pestilent venom, can neither duly digest and rarefy, nor govern and sufficiently discharge the infected humours; which for this reason putrefy and acquire a preternatural heat, and so excite a fever; which by reason of the foresaid secondary cause, is different and distinct from the plague, and a symptom of it. This is confirmed both by the maxims and authority of the ancients and moderns, as well as by practice, and evident examples.”
Thus it appears, both by fair reasoning by induction from facts, and from the authority of the greatest physicians, that the plague is certainly a disease by itself, and entirely distinct from all others. Hence it follows, that, though we could investigate the causes of fever in their utmost extent, we might still be ignorant of the true plague. That nothing, however, may be omitted, let us now consider what physicians have advanced on this subject, and what progress they have made in ascertaining the sources from whence so many direful calamities are derived.
In an inquiry of this kind, or indeed concerning any cause whatever, it is plain that the nature of the effect must be first understood. Fever then being aneffect, we must begin with investigating itsnature. But fever itself is only manifest by certain changes in the human body. Before we can investigate the nature of fever, therefore, we must investigate the human body, and that in a manner very different from what we did before. We must now consider the sources of life; in what manner the vital principle acts upon the body, and by what means its motions can be disturbed, or how they may be rectified when once disordered, &c. &c.
The systems of medicine before the time of Boerhaave are now so generally exploded, that it is needless to take any notice of them; and the reputation of Boerhaave himself in this way seems to be almost expiring. His doctrines, nevertheless, merit some attention, because he takes into account a principle overlooked by succeeding theorists, viz. thecohesionof the parts of the body. That he did so is evident, from his having written upon the diseases of aweak and laxfibre, and the diseases of astrong and rigidfibre. In other respects he followed in a great measure the mechanical physicians of the former century. He therefore took but little notice of the nervous system, as being less subject, or indeed to appearance not at all subject, to the known laws of mechanics. The blood was more manageable. The microscopical discoveries of Lewenhoeck furnished an excellent foundation for his system. This celebrated observer had discovered, or fancied he had discovered, that the red part of the blood is composed of globules. Inaccurate indeed these globules must have been, since each of them was composed of six; four touching one another in the middle, with one above, and one below, thus. The serum was said to be composed of single globules, and by this attenuation it was supposed that the fluid, instead of red, appeared of ayellowcolour. Still, however, this was insufficient. Each of the yellow globules wasdiscovered(either by fancied observations or by conjecture, it matters not which) to be composed of six others, which, singly taken, might constitute the lymph or some other fluid; and thus, like the number of the Beast, we might go on by sixes to the end of the chapter, and solve all the phenomena of nature. In justice to the microscopists, however, it must be observed, that some of them have given a much less fanciful account of the structure of the blood than Lewenhoeck. Mr. Hewson found it composed of vesicles, or small bladder-like substances, with a black spot in the middle. These vesicles dissolved in pure water, but kept their original form, which he says was as flat as a shilling, when a small portion of neutral salt was added to the fluid. The solid particles he supposed to be producedby the lymphatic system; the black particles by the spleen.
The supposed observations of Lewenhoeck were of considerable use to Boerhaave in the forming of his system of medicine, though they seem not to have accorded very well with his doctrine of lentor or viscidity in the blood. But, let this be as it will, having laid it down as the foundation of his theory, that the diseases of the body proceeded from too great a laxity of the fibres, or from too great a rigidity of them, and a great many from thislentor, his practice was accordingly directed to such medicines as he imagined would remove these supposed causes of disease. As the lentor of the blood was one of his favourite suppositions, he was therefore perpetually at war with this imaginary enemy, and dealt very much in saponaceous medicines with a view to break it down. But here it is evident that this great man was mistaken, even though we should allow the existence of lentor as much as he pleased. The viscidity,lentor, or any other state of the blood, is aneffectof something. It is part of that state into which the body is brought by the disease. The efforts of the physician therefore ought to be against that which produces the lentor; for, unless this be done, the cause of the disease must perpetually counteract the medicines by producing new lentor as fast as they destroy it; and besides, must have greatly the advantage of the physician, by being already in possession of the whole mass of blood, while the medicines can only enter it very gradually, and that by the stomach and lacteals, instead of being instantly mixed with it, and exerting their power immediately upon the fluid itself.
But besides this mistake, which is common to other systems, Boerhaave’s lentor has been denied, and that upon such strong grounds that it is now universally exploded. Another system quickly succeeded, in which every thing was managed by the nerves. This was introduced by Hoffman, adopted, and perhaps improved, by Dr. Cullen, under whose auspices it acquired such a degree of celebrity, that for a long time it was dangerousto write or speak against it; and the person who had the audacity to do so underwent a kind of medical proscription from the Edinburgh College and all its students. According to this celebrated theorist, the brain is that part of the body first formed in the embryo; it may be seen with nerves proceeding; from it long before the heart or any blood-vessel belonging to it is visible. Hence we are to conclude that this part is necessary to the existence of every other part of the body, though it doth not appear that they are essentially necessary to its existence. The superiority of the nerves to all other parts being thus established, the Doctor undertook to prove that all other parts of the body were formed from them; that the body is nourished immediately from them, and in short that the whole body is in such subjection to the nervous system, that, except for the mere purpose of distending the vessels, we can scarcely know for what end the blood exists; since the nerves can alter its consistence, or that of any of the fluids secreted from it, by a mere affection of that system, without any thing either added to or taken from the vital fluid.