CHAPTER VI.OF THE BLOOD.
Physical characters of the blood: colour, fluidity, specific gravity, temperature: quantity—Process of coagulation—Constituents of the blood: proportions—Constituents of the body contained in the blood—Vital properties of the blood—Practical applications.
Physical characters of the blood: colour, fluidity, specific gravity, temperature: quantity—Process of coagulation—Constituents of the blood: proportions—Constituents of the body contained in the blood—Vital properties of the blood—Practical applications.
211. Supposing the human body to have been built up in the manner now described, and to be in the full exercise of all its functions, the integrity of its various structures is maintained, and their due action excited by the blood. Out of this substance is formed the blandest fluid, as the milk, and the firmest solid, as the compact bone. The heart, capable of untiring action, as long as the blood is in contact with its internal surface, becomes immovable soon after the supply of this fluid is withdrawn; and in less than one minute from the time it ceases to flow in due quantity and of proper quality through the vessels of the brain, the eye is no longer capable of seeing, nor the ear of hearing, nor the brain of carrying on any intellectual operation.
212. At the moment, and for some time after it has issued from its vessel, the appearance of theblood is that of a thick, viscid, and tenacious fluid; yet it is essentially a solid, composed of several substances, each possessing its own distinct and peculiar properties, the relation and combination of which cannot be considered without exciting the feeling that our admiration of the structure of the animal frame ought not to be confined to the mechanism of its solid parts, but that the whole is admirable, from the common material of which it is composed, to its most delicate and elaborate instrument.
213. The colour of redness is universally associated with the idea of blood; but redness of colour is not essential to blood. There are many animals with true, yet without red, blood; and there is no animal in which the blood is red in all the parts of its body. The blood of the insect is transparent; that of the reptile is of a yellowish colour; that of the fish, in the greater part of its body, is colourless. Even the red blood of the human body is not equally red in every part of it, there being two distinct systems of blood-vessels, distinguished from each other by carrying blood of different colours.
214. In the state of health, the specific gravity of human blood, water being 1000, is 1080; from which standard it is capable of varying from 1120, the maximum, to 1026, the minimum.
215. The natural temperature of the human blood is 98°. From this it is capable of varyingfrom 104°, the maximum, to 86°, the minimum; these changes being always the effect of disease.
216. It is estimated that the fluids circulating in the adult man amount to about fifty pounds; of these it is calculated that twenty-eight consist of red blood.
217. Fluid and homogeneous as the blood appears while flowing in its vessel, when a mass of it is collected and allowed to stand at rest, it soon undergoes a very remarkable change. First, a thin film is formed upon its surface; this is followed by the conversion of the whole mass into a soft jelly: this jelly separates into two portions, a fluid and a solid portion. The solid portion again separates into two parts, into a substance of a yellowish-white colour, occupying the upper surface, and into a red mass always found at the under surface.
218. The process by which the constituents of the blood are thus spontaneously disunited, and afforded in a separate form, is denominatedCOAGULATION; the fluid portion separated by the process is termed theSERUM; the solid portion theCOAGULUMorCLOT; the white substance forming the upper part of the clot, theFIBRIN; and the red mass forming the under part of it, theRED PARTICLES.
219. Probably the process of coagulation commences the moment the blood leaves its living vessel. In three minutes and a half it is visible to the eye; in seven minutes the mass is formedinto a jelly; in from ten to twelve minutes the serum separates from the clot; in about twenty the clot is divided into fibrin and red particles, when the coagulation is complete; but occasionally the clot continues to grow firmer and firmer for the space of twenty-four hours.
220. As soon as the coagulation commences, and during all the time the blood preserves its heat, an aqueous vapour arises from it, termed theHALITUS. The halitus consists of water holding in solution a small quantity of animal and saline matter, which communicate to it a fœtid odour of a strong and peculiar nature, manifest on approaching a slaughter-house, and still more manifest in the slaughter-house of human beings, a field of battle.
221. During the process of coagulation, as in every other in which a fluid is converted into a solid, caloric is evolved.
222. During the process of coagulation carbonic acid is also extricated.
223. The process of coagulation affords three distinct substances, the chief constituents of the blood, namely, serum, fibrin, and red particles.
224. The serum, the fluid portion of the blood, when obtained perfectly pure, is of a light straw colour, tinged with green. Its taste is saline, and its consistence adhesive. It is composed principally of water holding in solution animal and saline matter. The animal matter gives it its adhesiveconsistence, and the saline its peculiar salt taste. The chief animal matter contained in it is the proximate principle termed albumen, which may be separated from the water that holds it in solution by the application of heat and by certain chemical agents. Heat being applied, when the temperature reaches 160°, fluid serum is converted into a white opaque solid substance of firm consistence. This is found to be albumen, which may be also separated from the watery portion by the application of spirits of wine, acids, oxymuriate of mercury, and several other chemical substances. The quantity of albumen contained in 1000 parts of serum varies from about 78, the maximum, to 58, the minimum.
225. If the albumen yielded by the serum be subjected to pressure, or be cut into small pieces, there flows from it a watery fluid which is termed the serosity. In meat dressed for the table, the serum of the blood contained in the blood-vessels is converted by the heat into solid albumen, from which, when cut, the serosity flows in the form of gravy.
226. Besides albumen, serum holds in solution both a fatty and an oily matter, in the proportion of about one part of each to 1000 parts of serum. The proportion of its saline substances is about ten in 1000 parts. According to M. le Canu, who has made the most recent chemical analysis of serum, 1000 parts contain, of
227. All the animal and saline matter held in solution in the serum being removed, the fluid that remains is water, the proportion of which in 1000 parts varies from 853, the maximum, to 779, the minimum.
228. The second constituent of the blood, the fibrin, is the most essential portion of it, being invariably present, whatever other constituent be absent. While circulating in the living vessel, fibrin is fluid and transparent; by the process of coagulation, it is converted into a solid and opaque substance of a yellowish white colour, consisting of stringy fibres, disposed in striæ, which occasionally form a complete net-work (fig. CXI.). These fibres are exceedingly elastic. In theirgeneral aspect and their chemical relations they bear a close resemblance to pure muscular fibre, that is, to muscular fibre deprived of its enveloping membrane and of its colouring matter, and they form the basis of muscle. According to M. le Canu, the proportion of the fibrin varies from seven parts in 1000, the maximum, to one part in 1000, the minimum, the medium of twenty experiments being four parts in 1000.
Fig. CXI.A portion of the fibrin of the blood, showing its fibrousstructure and the striated or net-like arrangement of itsfibres.
A portion of the fibrin of the blood, showing its fibrousstructure and the striated or net-like arrangement of itsfibres.
229. The third constituent of the blood, the matter upon which its red colour depends, though, as has been stated, entirely absent in certain classes of animals, and in all animals in some parts of their body, seems to be essential, at least to the organic organs, whenever they perform their functions with a high degree of perfection. Thus in the lowest class of vertebrated animals, the fish,while the principal part of its body receives only a colourless fluid, its organic organs, as the heart, the gills, the liver, are provided with red blood.
230. The red matter, wherever present, is invariably heavier than the fibrin, and consequently, during the process of coagulation, it gradually subsides to the lower surface, and is always found forming the bottom of the clot. Its proportion to the other constituents varies very remarkably, the maximum being 148, the minimum 68, and the medium 108, in 1000 parts of blood.
231. All observers are agreed that the red matter of the blood consists of minute particles, having a peculiar and definite structure; but in regard to the nature of that structure, there is considerable diversity of opinion, which is not wonderful, since the particles in question are so minute that they can be distinguished only by the microscope, and since, of all microscopical objects, they are perhaps the most difficult to examine, because, being soft and yielding, their figure is apt to change, and because there is reason to suppose that their substance is not uniform in its refractive power.
232. The earlier observers describe the red particles as being of a globular figure, and accordingly name them globules. They conceive that each globule consists of a central solid particle, enveloped in a transparent vesicle. Recently, Sir Everard Home and Mr. Bauer in this country, and MM. Prevost and Dumas on the continent, have revivedthis opinion, and describe the red particle as consisting of a central solid white corpuscle contained in an external envelop of a red colour. When the blood is observed with the microscope in a living animal, flowing in its vessels, only two substances can be distinguished, namely, a transparent fluid and the red corpuscles. MM. Prevost and Dumas contend that these two substances are the only component parts of the blood. When the blood coagulates, they conceive that the red envelop separates from the central white corpuscle; that these white corpuscles unite together; that the aggregates resulting from this combination are disposed in the form of filaments, which filaments constitute the fibrin, while the red matter at the bottom of the clot is nothing but the disintegrated envelops of the central particle. But this view is not the common one. In general, physiologists conceive the fibrin to be one constituent and the red particles to be another constituent of the blood. Mr. Lister, who has successfully laboured to improve the microscope, and who, together with his friend Dr. Hodgkin, have very carefully examined with their improved instrument the red particles, contend that the figure of these bodies is not globular, although they state that the instant the particles are removed from the living blood-vessels many things are capable of making them assume a globular appearance; such, for example, as the application of water. With a rapidity which, inspite of every precaution, the eye in vain attempts to follow, the particles change their real figure for a globular form on the application of the smallest quantity of pure water; while, if the water contain a solution of saline matter, little alteration is occasioned in the figure of the particles. According to these observers, the red particles are flattened cakes, having rounded and very slightly thickened margins (fig. CXII. 1). The thickness of the margin gives to both surfaces the appearance of a slight depression in the middle (fig. CXII. 1), so that the particles bear a close resemblance to a penny piece. There is no appearance of an external envelop. The circular and flattened cake is transparent; when seen singly it is nearly if not quite colourless (fig. CXII. 1); it assumes a reddish tinge only when aggregated in considerable masses.
Fig. CXII.1. A particle of the human blood as it appears whentransparent and floating; 2. the same dry, seen as opaque,illuminated by a leiberkuhn; 3. the same as it appearswhen half the leiberkuhn is darkened; 4. a particle of thefrog's blood floating; 5. the same seen on its edge. Allthe above objects are magnified 500 diameters[5]
1. A particle of the human blood as it appears whentransparent and floating; 2. the same dry, seen as opaque,illuminated by a leiberkuhn; 3. the same as it appearswhen half the leiberkuhn is darkened; 4. a particle of thefrog's blood floating; 5. the same seen on its edge. Allthe above objects are magnified 500 diameters[5]
233. The red particle of the human blood is circular (fig. CXII. 1, 2, 3).It is circular also in all animals belonging to the class mammalia; but in the three lower classes of vertebrated animals, the bird, the reptile, and the fish, it is elliptical (fig. CXII. 4, 5).
234. The magnitude of the red particle of the human blood is variously estimated from the two-thousandth to the six-thousandth part of an inch in diameter. Bauer estimates it at the two-thousandth, Hodgkin and Lister at the three-thousandth, Kater at the four-thousandth, Wollaston at the five-thousandth, and Young at the six-thousandth part of an inch. Its magnitude is uniformly the same in all individuals of the same species, but differs exceedingly in the different classes. The elliptical particles are larger than the circular, but proportionally thinner; larger in fishes than in any other class of animals, and largest of all in the skate.
235. When perfect and entire, the red particles indicate a disposition to arrange themselves in a definite mode. They combine spontaneously into columns of variable length (fig. CXIII.). In order to observe this tendency, a small quantity of blood, the moment it is taken from its living vessel, should be placed between two strips of glass or covered with a bit of talc and placed under the microscope. When thus arranged, a considerable agitation at first takes place among the particles. As soon as this motion subsides, theparticles apply themselves to each other by their broad surfaces, and thus form piles or columns of Considerable length (fig. CXIII.). The columns often again combine one among another, the end of one being attached to the side of another, sometimes producing very curious ramifications (fig. CXIII.). In like manner, the elliptical particles apply themselves to each other by their broad surfaces, but they are not so exactly matched as the circular, one particle partially overlapping another, so that they form less regular columns than the circular.
Fig. CXIII.Columnar arrangement which the particles of the humanblood assume immediately after it is drawn from its vessel.
Columnar arrangement which the particles of the humanblood assume immediately after it is drawn from its vessel.
236. The red particles, as far as is known, constitute a distinct and peculiar form of animal matter: the red colour, according to some, depending on an impregnation of iron; according to others, on an animal substance of a gelatinous nature.
237. The exact proportion of the different substancescontained in the blood, according to the most recent analysis of it, that by M. le Canu, is as follows, namely,
238. From the results of this analysis it is manifest that all the proximate principles of which the different tissues are composed exist in the blood, namely, albumen, the proximate principle forming the basis of membrane; fibrin, the proximate principle forming the basis of muscle; fatty matter, forming the basis of nerve and brain; and varioussaline and mineral substances, forming a large part of bone, and entering more or less into the composition of every fluid and solid.
239. The blood, which contains all the proximate constituents of the body, and which, by distributing them to the various tissues and organs, maintains their integrity and life, is itself alive. The vitality of the blood is proved,—
240. i. By its undergoing the process of death, which it does just as much as the heart or the brain, every time it is removed from the body. While flowing in its living vessel, the blood is permanently fluid. Its fluidity depends on a force of mutual repulsion exerted by its particles on each other. That repulsive force is a vital endowment, probably derived from the organic nerves so abundantly distributed to the inner coat of the blood-vessels. When this vital influence is withdrawn, which happens on the removal of the blood from its vessel, the mass is no longer capable of remaining fluid; the fibrin is converted into a solid; the red particles, instead of repelling, attract each other, forming the crude aggregate at the bottom of the clot; coagulation is thus a process of death; its commencement indicates a diminution of the vital energy of the blood; during its progress that energy is constantly growing less and less; the blood is dying; and when complete, the blood is dead.
241. Hence in every state of the system in which the vital energy of the blood is preternaturallyincreased, coagulation is proportionably slow; in every state in which its energy is diminished, coagulation is rapid. By copious and repeated blood-letting, the vital energy is rapidly exhausted. The effect of blood-letting on coagulation is determined by experiments instituted for the express purpose of ascertaining it. Blood was received from a horse at four periods, about a minute and a half intervening between the filling of each cup.
242. In like manner three cups were filled with the blood of a sheep, at the interval of half a minute.
The same result was obtained in blood taken from a human subject. A pound and a half of blood was removed from the arm of a woman labouring under fever, a portion of which, received into a tea-cup on the first effusion, remained fluid for the space of seven minutes; a similar quantity, taken immediately before tying up the arm, was coagulated in three minutes thirty seconds. These experiments demonstrate that coagulationis rapid or slow as the vital energy of the blood is exhausted or unexhausted, or that in proportion to the degree of life possessed by the blood is the space of time it takes in dying.
243. This result is referable to the principle already shown to be characteristic of living substance, —namely, the power of resisting, within a certain range, the ordinary influence of physical agents. The operation of this power is illustrated in a beautiful manner in a series of experiments performed by Mr. Hunter on the egg and on blood. This physiologist exposed a live, that is, a fresh egg to the temperature of the 17th and the 15th degrees of Fahrenheit; it took half an hour to freeze it. The egg was then thawed and exposed to 10° less cold, namely, to the 25th degree of Fahrenheit; it was now frozen in a quarter of an hour. A living egg and one that had been killed by having been first frozen and then thawed, were put together into a freezing mixture at 15°: the dead was frozen twenty-five minutes sooner than the living egg. The undiminished vitality of the fresh egg enabled it to resist the low temperature for the space of twenty-five minutes; the vitality of the frozen egg having been destroyed, it yielded at once to the influence of the physical agent. On subjecting blood to analogous experiments, the result was found to be the same. Blood immediately taken from the living vessel, and blood previously frozen and then thawed, being exposedto a freezing mixture, a much shorter period and a much less degree of cold were required to freeze the latter than the former.
244. ii. The vitality of the blood is proved by the change it undergoes in becoming a constituent part of an organized tissue. The blood conveys to the several tissues the constituents of which they are composed; each tissue selects from the mass of blood its own constituents and converts them into its own substance, in which conversion, since the blood always goes to the tissue in a fluid form, the blood must necessarily pass from a fluid into a solid. In the vessels the vital endowment of the blood maintains it permanently fluid; in the structures the same power makes it and keeps it solid. One and the same substance in one and the same body, in one part is always fluid, in another always solid; the fluid is every moment passing into the solid and the solid into the fluid, without intermixture and without interference. Nothing analogous to this is ever witnessed in inorganic matter, in physical mechanism; it is peculiar to the organized body and distinctive of the mechanism of life. Sometimes in physical mechanism we can perceive the mechanical arrangements and distinctly trace them from beginning to end: in vital mechanism, even when we can discern the mechanical arrangements, we can seldom trace them beyond a step or two, and never from beginning to end; but arrangement and adaptation weknow there must be in that which goes beyond, no less than in that which keeps within, our perception, and we ought scarcely to question the existence of adjustments, because they elude our sense, when probably the very reason why they do so is that their delicacy and perfection immeasurably exceed any with which sense has made us acquainted.
245. iii. The vitality of the blood is proved by the process of organization. We can trace only a few steps of this process, but these are sufficient to establish the point in question. Blood effused from living vessels into the substance, or upon the surface of living organs, solidifies without losing vitality. If a clot of blood be examined some time after it has thus become solid, it is found to abound with blood-vessels. Some of these vessels are obviously derived from the surrounding living parts. The minute vessels of these parts, as can be distinctly traced, elongate and shoot into the clot. The clot thus acquires blood-vessels of its own. By degrees a complete circulation is established within it. The blood-vessels of the clot act upon the blood they receive just as the vessels of any other part act upon their blood, that is transform it into the animal matter it is their office to elaborate. In this manner a clot of blood is converted into a component part of the body, and acquires the power of exercising its own peculiar and appropriate functions in the economy.
246. But while, in this process, some of the vessels of the clot can be distinctly traced from the surrounding living parts, others appear to have no communication with those parts, at all events no such communication can be traced. These vessels, the origin of which cannot be found external to the clot, are supposed by some physiologists to be formed within it. Within the living egg, during incubation, certain motions or actions are observed spontaneously to arise, which terminate in the development of the chick. Analogous motions arising within the clot terminate, it is conceived, in the development of blood-vessels. According to this view, a simultaneous action takes place in the clot, and in the living part with which it is in contact; each shooting out vessels which elongate, approximate, unite, and thus establish a direct vital communication. Whether this view of the process of organization be the correct one or not does not affect the present argument. It is certain that a clot of blood surrounded by living parts becomes organized; it is certain that no dead substance surrounded by living parts becomes organized; it follows that the blood possesses life.
247. Health and life depend on the quantity, quality, and distribution of the blood. The chief source from which the blood itself is derived is the chyle: hence too much or too little food, or too great or too little activity of the organs that digest it, may render the quantity of the blood preternaturallyabundant or deficient; or though there be neither excess nor deficiency in the quantity of nourishment formed, parts of the blood which ought to be removed may be retained, or parts which ought to be retained may be removed, and hence the actual quantity in the system may be superabundant or insufficient.
248. The relative proportion of every constituent of the blood is capable of varying; and of course in the degree in which the healthy proportion is deranged, the quality of the mass must undergo a corresponding deterioration. The watery portion is sometimes so deficient, that the mass is obviously thickened; while at other times the fluid preponderates so much over the solid constituents, that the blood is thin and watery. The albumen, the quantity of which varies considerably even in health, in disease is sometimes twice as great, and at other times is less than half its natural proportion. In some cases the fibrin preponderates so much, that the coagulum formed by the blood is exceedingly coherent, firm and dense; in other cases the quantity of fibrin is so small, that the coagulation is imperfect, forming only a soft, loose and tender coagulum, and in extreme cases the blood remains wholly fluid. When the vital energy of the system is great, the red particles abound; when it is depressed, they are deficient. In the former state, they are of a bright red colour; in the latter, dusky, purple, or even black. Whenthe depression of the vital energy is extreme, the power of mutual repulsion exerted by the particles would seem to be so far destroyed as to admit of their adhering to each other partially in certain organs; while in other cases they seem to be actually disorganised, and to have their structures so broken up, that they escape from the current of the circulation as if dissolved in the serum, through the minute vessels intended only for the exhalation of the watery part of the blood. This fearful change is conceived to have an intimate connexion with a diminution of the proportion of the saline constituents. Out of the body, as has been shown, the red particles change their figure instantaneously, and are rapidly dissolved when in contact with pure water; while they undergo little change of form if the water hold saline matter in solution. It would seem that one use of the saline constituents of the blood is to preserve entire the figure and constitution of the red particles. It is certain that any change in the proportion of the saline constituents produces a most powerful effect on the condition of the red particles. It is no less certain that changes do take place in the proportion of the saline constituents. In the state of health, the taste of the blood is distinctly salt, depending chiefly on the quantity of muriate of soda contained in it. In certain violent and malignant diseases, such, for example, as the malignant forms of fever, and more especially that form of it termed pestilentialcholera, this salt taste is scarcely, if at all, perceptible; and it is ascertained that, in such cases, the proportion of saline matter is sensibly diminished.
249. The quality of the blood may be also essentially changed by the disturbance of the balance of certain organic functions: digestion, absorption, circulation, respiration, are indispensable to the formation of the blood and to the nourishment of the tissues. Absorption, nutrition, secretion, circulation, render the blood impure, either by directly communicating to it hurtful ingredients, or by allowing noxious matters to accumulate in it, or by destroying the relative proportion of its constituents. Organs are specially provided, the main function of which is to separate and remove from the blood these injurious substances. Organs of this class are called depurating, and the process they carry on is denominated that of depuration. The lungs, the liver, the kidneys, are depurating organs, and one result at least of the functions they perform is the purification or depuration of the blood. If the lung fail to eliminate carbon, the liver bile, the kidney urine, carbon, bile, urine, or at least the constituents of which these substances are composed, must accumulate in the blood, contaminate it, and render it incapable of duly nourishing and stimulating the organs.
250. But though the blood be good in quality and just in quantity, health and life must stilldepend upon its proper distribution. It may be sent out to the system too rapidly or too slowly. It may be distributed to different portions of the system unequally; too much may be sent to one organ, and too little to another: consequently, while the latter languishes, the former may be oppressed, overwhelmed or stimulated to violent and destructive action. In either case health is disturbed and life endangered.
251. Of the mode and degree in which food, air, moisture, temperature, repletion, abstinence, exercise, indolence, influence the quantity, quality, and distribution of the blood; of the mode in which the condition of the blood modifies the actions both of the organic and the animal organs; of the reason why health and disease are wholly dependent on those states and actions, a clear and just conception may be formed when the several functions have been described, and the precise office of each is understood.