OF ANIMAL CHEMISTRY.SECTION ONE.
drop-cap
Thepurpose of the present chapter, so far as our knowledge extends, is to describe the chemical history of those bodies which are characterized as being rather organized than organic; as constituting not merely a product of the vital operations of the being, but the mechanism itself by which these vital operations are carried on; as making part of the tissues essential to its proper organization and life; and as being, while in connection with the animal and participating in its life, protected from the truly chemical reactions of their proper elements, which after the death of the animal, especially when in contact with air or water, rapidly assume simpler forms of union, and breaking up the complex animal tissue into a crowd of binary compounds, under the change well known as putrefaction.
In connection with these substances which form the basis of the organs and tissues of the animal frame, will be brought under survey the processes by which, from the atmosphere or from the materials of our food, the substance of our organs is continually renewed, their growth provided for, and the conditionsnecessary for the continuance of life and health maintained. The following elucidation of the materials which enter into the composition of the human body is of extreme importance, as it will help to demonstrate why the chemicals employed in the former processes of embalming have been selected in preference to others.
Of Fibrine.—This substance constitutes the basis of the muscular tissue, and forms an important constituent of the blood. In the latter it exists dissolved during life, but separates after death or extraction from the body, producing, with the coloring material, the phenomenon of coagulation. In the muscles the fibrine is arranged in a truly organized and living condition, constituting the contractile fibres, in which it is so interwoven with nervous and vascular filaments as to render its isolation impossible. To obtain pure fibrine, therefore, we have recourse to blood, which, if immediately on being drawn it be briskly agitated with a little bundle of twigs, does not coagulate, but the fibrine is deposited on the twigs in soft, tenacious masses, which, being washed to remove any adhering coloring matter, and digested in alcohol and ether to remove any traces of fatty substances which may adhere to it, constitute pure fibrine; which may be dried by a gentle heat, and appears then as a yellowish, opaque mass, hard, tasteless and inodorous. If it be at all transparent, this results from traces of adhering fat. It is insoluble in water, alcohol and ether; it absorbs, however, so much water as to trebleits weight, and thereby recovers the volume, softness and flexibility it possessed before being dried.
If sulphate of soda or nitrate of potash be added to newly drawn blood, its coagulation is prevented; and if fibrine be digested in a strong solution of nitre, it dissolves, forming a thick liquid, which is coagulated by heat, by alcohol, by acids, and is precipitated by thesalts of mercury,leadandcopper, and by yellow prussiate of potash. This property of fibrine will again come under our notice.
Of Albumen.—This substance is even more extensively distributed through the animal frame than fibrine. Like fibrine, it exists in two conditions, one soluble and one insoluble in water; but whereas the fibrine becomes insoluble almost instantly on being withdrawn from the body, albumen may retain that state for an indefinite time, and its history is therefore more complete. In its soluble form it exists in the blood, in the serous secretions, in the humours of the eye; in the soluble or coagulated form it constitutes a portion of most of the solid tissues.
Soluble Albumen.—This is obtained in the solid form by evaporating to dryness, at a temperature which does not exceed 120°, the serum of blood; the dry mass is yellow, transparent, hard, tough, and contains, besides the albumen, the salts and some other constituents of the blood in minute quantities; these are extracted by digestion in alcohol and ether, which leave the albumen pure. When thus completely dry it maybe heated beyond 212° without passing intothe coagulated condition; if digested in cold water it gradually swells up and finally dissolves. This solution, when heated to a temperature between 140° and 150°, coagulates; if dilute, the solution may even be heated to 165° without coagulating, and when present in very small quantity the albumen may not separate until the water boils.
When once coagulated in this manner, albumen is totally insoluble in water; it is then changed into its second form. The solution of albumen is precipitated byalcohol, byacidsandmetallic salts, exactly as the solution of fibrine in saltpetre; the only distinction that can be drawn between the two is that the saline solution of fibrine is partially decomposed by the addition of a large quantity of water.
The precipitates yielded by a solution of albumen with metallic salts are mixture of two distinct substances, one a compound of albumen with the acid, the other a compound of albumen with the metallic oxide; the former is generally somewhat soluble, the latter insoluble, and hence results the application of albumen as an antidote to mineral poisons, as corrosive sublimate and blue stone.
Albumen is also coagulated by many organic bodies, as tannic acid and creosote, which acts catalytically, as a very minute quantity of it coagulates a large quantity of albumen, without entering into combination with it.
Of the Gelatinous Constituents of the Tissues.—When the skin, cellular or serous, tissues, tendons, and someforms of cartilage, as that of bones, are boiled in water, they dissolve in great part and form a solution which gelatinizes on cooling. Some of these tissues, as the skin, dissolve easily and almost completely; others dissolve but partly, and leave behind a quantity of coagulated albumen. In most kinds of cartilage a very prolonged boiling is necessary to extract a sensible quantity of gelatine. These various tissues are thus found to consist of albumen and gelatine, united in various proportions, and each presenting various degrees of condensation of texture; but by boiling they may be completely separated from each other.
Gelatine is insoluble in alcohol and ether. When a solution of gelatine is long exposed to the air, it undergoes a commencement of putrefaction, and loses its property of gelatinizing.
The action of reagents on gelatine is in some cases of high interest, it is not precipitated by solutions of either ordinary or basic alum, but if a solution of common salt be also mixed, the gelatine falls down, combined with alumina, as it decomposes the muriate of ammonia which is then formed. On this principle is founded the manufacture of white leather, by a kind of tanning with alum.
The most important compound of gelatine is that with tannic acid, which constitutes ordinary leather; this reaction is so distinct that one part of gelatine in five thousand of water is at once detected by the infusion of galls.
Many chemists consider that gelatine is merely aproduct of the decomposition of albumen and fibrine by boiling water, and not a true constituent of the tissues; but this idea is thought to be incorrect, on the following grounds: First, pure fibrine or albumen gives no gelatine by boiling; second, in the process of tanning, the tannic acid combines with gelatine in a skin which has never been boiled; and third, that we can easily understand why some tissues give more gelatine than others by the different degrees of condensation of their structure. But it is rather considered that gelatine bears the same relation to the tissues of the skin or cellular membrane that protein does to the fibrine of the blood, being really a product of its death and decomposition,though the only representative of it which we can have.
Of the Fatty Constituents of the Tissues.—The fatty bodies, although contributing essentially to the support of the animal frame, are mere secretions, and do not form any portion of its organized tissues. The substances properly included under the present head are the constituents of the nervous tissue, such as it is found in the brain, the spinal cord and the nerves.
In the composition of the brain, it is easy to distinguish three, perhaps five, distinct substances of a fatty nature; the most characteristic and important is called cerebrote; in composition it resembles albumen, containing a large quantity of nitrogen.
Saline, and Extractive Constituents of the Tissues.—We find in all the animal tissues small quantities of agreat variety of salts, the same as those which will be hereafter noticed as existing in the blood, to the presence of which in the substance of the tissues they are probably due. In the tissue of the bones and teeth, however, these saline matters are deposited in much greater quantities, and in disease and old age bony deposits occur in all those tissues, which yield true gelatine on boiling. The composition of the bones will be hereafter noticed.
Of the Composition of the Tissues and of the Secretions in Health and Disease.—Having described thus individually the constituents of the tissues, we shall now present such results as have been hitherto obtained as to the quantitative composition of the organized tissues formed by their reunion, their secretory products and morbid alterations.
The skin of animals is a congeries of finely constructed organs, sensitive and secretory, imbedded in a peculiar tissue, which is one of those most yielding gelatine, whence the process of tanning skins. On the surface of the skin there is secreted a substance, which, though varying in anatomical structure and appearance exceedingly, as it forms the fine epidermis, the nails, the hair, etc., is yet throughout all their shapes identical in chemical character, and may be described as the same substance. The principal mass of hair is composed of the same substance as horn, but the color is due to an oil which may be extracted by ether. If by virtue of the sulphur contained in hair a solution of litharge in some limestone waterblackens it, a solution of nitrate of silver will also blacken the hair, but by a deposition of the metal.
The perspiration from the skin varies in nature according to the part of the body; it is generally acid, contains traces of albumen, fatty matter and the salts of the blood; it often contains, also, an odoriferous, volatile principle, characteristic of the animal by which it is secreted.
Cellular and Serous Tissues.—These tissues are constituted of gelatinous materials similar to that in the skin, and hence dissolve by boiling water, being converted into gelatine. In the natural condition of these membranes their surface is moistened by a watery liquid, which, accumulating in excessive quantity, gives rise to the dropsies of the cavities, or of the cellular tissues. This serum of the cavities is clear and colorless. The cells of the cellular tissues, in which fat is usually deposited, are often filled up by an albuminous material having considerable analogy with casein; it is thus that the diffused hardening of the cellular tissue and the local white tumors have their origin.
Of the Muscular Tissue.—From what has been already said of fibrine, it is evidently the essential element of the muscular tissues, and forms with water almost the whole of their parts.
Of the Bones.—In vertebrated animals with osseous skeletons the earthy material, in all cases, consists principally of phosphate of lime, with phosphate ofmagnesia, carbonate of lime and soda. By digesting a bone in dilute muriatic acid, all of these inorganic salts are removed, and the cartilage remains, preserving perfectly the form of the bone.
The teeth present, in their combinations, the greatest analogy to bone; the principal and organized substance of the teeth is indeed true bone, containing indeed less cartilage and more phosphate of lime than other bones. The enamel, which is an inorganic secretion from the surface of the long tooth, is almost destitute of any animal matter.
Of the Composition of the Blood.—Blood is, in the higher classes of animals, an opaque, thick, red fluid; it has a salty and nauseous taste, and a peculiar smell, resembling that of the animal whence it has been derived.
When the blood of any red blooded animal is allowed to rest, it gradually forms a soft jelly, from which, after some time, a thin yellowish fluid (serum) separates, while the red jelly or coagulum contracts in volume and acquires great consistence. If this coagulation of the blood takes place slowly, the upper portion of the coagulum becomes white or pale yellow; forming thus, the buffy coat. There is no doubt that the blood, while in connection with the animal, participates in its life, and the phenomena of coagulation are to be referred to a new arrangement of its materials consequent on the loss of that vitality.
The serum of the blood, when coagulation has been perfect, is of a yellowish, sometimes greenish,color; its taste is dull and salty; it is thick fluid, like olive oil; when heated to 140° it coagulates.
If we examine under the microscope the appearance presented by blood, we find that it consists of a great number of red particles swimming in a nearly colorless liquor. These red particles are flattened disks; in man they are round. Their size is variable, being in man from one four-thousandth to one eight-thousandth of an inch in diameter, but larger in other animals.
The blood contains a large quantity ofalbumen, partly dissolved and remaining in the serum after coagulation, partly in a solid state, forming the great mass of the globules.
In the living body the blood also contains fibrine in solution, but this separates soon after extraction from the body; it assumes a solid form, and investing, as a sponge, the red globules, forms with them the coagulum.
The fibrine is thus the element active in the coagulation of the blood, the globules being but passively engaged in it. In addition to this essential organic element, the blood contains a variety of salts, as common salt, phosphate of magnesia, ammonia and lime, lactates of soda and magnesia. The best analyses of the blood are those of Lecanu, and the results for blood and serum are that they contain, in the human subject of each sex:
The fatty substance of the blood is a mixture of cholesterine with stearic and oleic acid and a peculiar fatty substance termed seroline, the history of which is yet incomplete. None of the fats of the brain, however, seem to exist in the blood.
The chemical history of fibrine and albumen having been already given, it remains only to describe the peculiar coloring matter, for the most accurate knowledge we possess concerning which, we are indebted to Lecanu’s elaborate researches on the blood.
Pure hematosine or coloring matter, when it is coagulated, is a dark brown mass, tasteless and inodorous; when heated it does not smell, but swells up and evolves ammoniacal products; it is insoluble in water, alcohol and ether;it forms, with the mineral acids, compounds which are insoluble in water but soluble in alcohol.
By caustic alkalies it is dissolved with a red-blood color, and these combinations are soluble in water, alcohol and ether. Hematosine contains neither phosphorus nor sulphur, but iron in large quantities. The state in which iron exists in hematosine has been, up to the present day, an object of much discussion among chemists; but with the knowledge we now possess of hematosine in its pure form, we must consider the iron to be an integral part of its organic constitution, as sulphur in albumen, or arsenic in alkarsine, and the opinion of its being oxydized and combined with the true organic element as a kind of salt can no longer be supported. If a solution ofhematosine be acted on by chlorine gas, a white, flocculent precipitate is produced, and the solution contains chloride of iron.
Although hematosine is the coloring principle of the globules of the blood, it is present but in very small quantity; one hundred parts of dried globules containing but four to five parts of hematosine; in the blood globule the hematosine exists in its uncoagulated state, and possesses properties somewhat different from those of its coagulated form.
A solution of the colored blood globules in water, when exposed to the air, becomes of a brighter red color, being thus partially arterialized; it iscoagulated also by alcohol and by acids; the hematosine then passes into the condition of insolubility, already described.
The colorless ingredient in the blood globules has already been spoken of as being albumen, with which, indeed it is identical in properties, but differ in some points. It has been termed globuline. In its uncoagulated condition it can not be separated from hematosine, and is there distinguishable from albumen, principally by being insoluble in even a very dilute saline solution, which dissolves albumen readily. It is, hence, that the globules of the blood swim unaltered in the serum, but are readily dissolved by pure water.
If the blood, when extracted from the vein, is received into a vessel containing a solution of glauber’s salt, coagulation is prevented, as the fibrine remains dissolved, and by filtering the liquor so obtained, theserum and water pass off and the globules remain, mixed only with little of the salt. The globuline cannot, however, be separated from hematosine, except by acids, which, as described in the preparation of hematosine, then combine with the globuline.
Alteration of the Blood in disease.—The examination of the state of the blood in disease, although presenting important relations to pathology and to practice, has been conducted in a manner too disconnected and superficial to produce any satisfactory results. This branch of chemical pathology has, however, been taken up by the illustrious Andral and Gavaret, who have published the result of the analysis of the blood in three hundred and sixty cases of disease.
Their researches have enabled them to recognize four classes of diseases, in which the composition of the blood is essentially altered, though in different ways.
The first class presents as a constant alteration, an increase in the quantity of fibrine; it includes diseases remarkably different in their locality and form, but all belonging to the class of acute inflammations in some cases of morbid deposition, as in tubercle and cancer, a similar increase in the quantity of fibrine is found, but it may be doubted whether it be due to abnormal growth or to the inflammatory action which accompanies it.
In the second class the fibrine remains stationary, or even diminishes in quantity, while the globules increasein proportion to the fibrine. The diseases which belong to this class, are, continued fevers without local inflammation, and some form of cerebral hemorrhages.
Cerebral Hemorrhages.—In the third class, the fibrine remaining unchanged, there is a remarkable diminution in the quantity of globules; of these diseases, chlorosis may be taken as an example, and in the fourth class it is no longer the fibrine or the globules which are the subject of the morbid change, but the quantity of the albumen in the serum is diminished; of this class of affections is Bright’s disease.
It has been observed, that in cholera the blood becomes so thick as to arrest the circulation, and contains from thirty to forty-five per cent. of solid matter; it is then, also, less strongly alkaline than healthy blood; this is connected probably with the matters vomited and evacuated, which are strongly alkaline, and contain a quantity of albumen.
The blood has been found, occasionally, in cases of Diabetes Mellitus, to contain traces of sugar. The great discordance of the results obtained, may result, perhaps, from the sugar contained in the blood only for a short time after meals, and then being rapidly evacuated by the kidneys. In the jaundice the green coloring matter of the bile has been found mixed with the blood.
Other observations of morbid constituents of the blood are too indefinite to justify me in occupying space with them.
Color of the Blood.—In the living body, the blood in the veins and arteries is well known to differ essentially in color; in the former being of a dark purple-red, in the latter of a bright vermilion color. The change from the venal to the arterial state occurs during the passage of the blood through the capillary vessels of the lungs, where it is exposed to the action of an extensive surface of atmospheric air; while the arterial blood, in traveling the general capillary system of the body, assumes the red, dark condition in which it is carried back to the heart by the veins. Yet, although the vital properties of the blood depend essentially upon this change of color, we are not able to connect it with any alteration in the composition of the constituents of the blood, or even in their relative proportions.
Arterial and venous blood contains sensibly the same quantity of water, fibrine, globules, albumen and salts; and, by analysis, the composition of those bodies is found to be identical, no matter what kind of blood they may be derived from. To trace the difference of nature between arterial and venous blood, it is therefore necessary to study it under different points of view than its approximate or elementary composition. So far as we have yet explained it, the air which has been employed in respiration, is found to have undergone an important change of constitution; its volume is but slightly, if at all, altered; but a quantity of oxygen has disappeared, and is replaced by carbonic acid, in generally equal volume.Air which has been once respired is found to contain from three to four per cent. of carbonic acid, and if the same quantity of air be continually breathed, the animal dies with all the symptoms of narcotic poisoning. When the carbonic acid has accumulated to from eight to ten per cent., the action of the air in expiration is therefore to remove carbon from the blood. The quantity so taken from the system in twenty-four hours is very large, and makes up the principal portion of that element which we take in with our food; yet, such is the activity with which its assimilation provides, that no perceptible change in the solid elements of the blood can be perceived.
It was, at one time, a much disputed point, whether the carbon so separated from the system was directly excreted from the lungs, and carried off as it were, by contact with the oxygen of the air, or whether the oxygen was first absorbed by the blood and carried by the circulation to every portion of the body, where it combined with the carbon, which was there present in excess, and the carbonic acid so produced, being dissolved by the venous blood, was thrown off on arriving at the surface of the atmosphere, in the lungs. The progress of science has, however, finally decreed in favor of the latter view, to which the fullest confirmation has been given by the careful and elaborate researches of Magnus.
Gases in the Blood.—It was found that both arterial and venous blood contain dissolved quantities of gases, oxygen, nitrogen and carbonic acid, whichamount to from one-tenth to one-twentieth the volume of the blood; the proportions of these two gases to each other are different in arterial and venous blood; the oxygen in arterial blood being about one-half of the carbonic acid, while in the venous blood it seldom amounts to more than one-fifth; the difference is greatest in young persons, and probably is proportional to their activity of nutrition.
The quantity of nitrogen appears to be the same in both kinds of blood, making from one-fifth to one-tenth of the gaseous mixture.
The physico-chemical conditions of respiration are simply explicable upon these results, by the principle of gaseous diffusion, the fine lining pulmonary membrane being permeable to gases. When the venous blood arrives at the surface of the lungs, a portion of the carbonic acid which it contains is evolved, and a quantity of oxygen gas absorbed in place of it; these two quantities are not necessarily equal at each moment, though ultimately they become so, and hence the volume of oxygen absorbed is generally, though not universally, equal to that of the carbonic acid given out. There appears, from the presence of nitrogen in equal quantity in both kinds of blood, to be an absorption and evolution of that gas, simply from physical laws, and independent of any application of it to the nutrition of the animal; hence the volume of nitrogen in air is sometimes increased, and at others diminished, by respiration, and a man evolves much nitrogen when respiring an atmosphere of oxygen andhydrogen, while it has been shown that the rate of nutrition of a man is proportionate to the quantity of nitrogen it receives as food, and that none of that principle is really assimilated from the air.
It is still by no means easy to decide upon the changes of color which occur in the blood during respiration; for this should appear connected, not merely with the presence of certain gases in the blood, but upon a true change in the composition of hematosine, which analysis cannot direct.
Stevens first attracted the attention upon the influence which saline bodies have upon the color of the blood. If dark, venous blood is put in contact with a solution of common salt, glauber salt, nitre, or carbonate of soda, it becomes as vermilion colored as if it had been truly arterialized; on the contrary, the presence of carbonic acid impedes this action, and gives to blood, so reddened by a salt, not in excess, the dark tint of venous blood.
If we consider, therefore, the arterial tint to be due to the material combination of the coloring matter with the saline constituents of the serum, this will be darkened, when, by passing through the capillary system, the blood takes up an excess of carbonic acid; and again, in the lungs, when the carbonic acid is replaced by oxygen, the vermilion color is restored, not by any active agency of the oxygen, but by the natural tint of saline hematosine becoming evident.
Although this theory of the change of color is by no means free from objection, it still appears to be better founded than any other that has been proposed.
Animal Heat.—The phenomena of respiration consisting mainly in the conversion of carbon into carbonic acid by union with oxygen, the heat which is developed in the body of all red blooded animals has been naturally referred to that source; and as we know that the change from the arterial to the venous condition of the blood occurs at every point of the system, the almost complete equality of temperature throughout the body in health is explained. That the great source of heat is the respiratory process, is abundantly proved by the temperature being highest in those animals, and in the same animal, at those periods when the circulation is most rapid and the quantity of air consumed the greatest. But it has been calculated that the heat evolved by the combustion of the quantity of carbon thrown off from the body in twenty-four hours is no more than eight-tenths of the quantity generated in the body during that time, and the origin of the remainder must be found in the action of the muscles and the nervous power, which appears of itself to be a distinct source of animal heat.