Читать книгу Anatomy and Embalming - Charles Otto Dhonau - Страница 52

—The blood of the body is contained in a practically closed system of tubes, the blood vessels, within which it is kept circulating by force of the heart beat. It is usually spoken of as the nutritive liquid of the body, but the functions may be stated explicitly, although still in quite general terms, by saying that it carries to the tissues food stuffs after they have been properly prepared by the digestive organs; that it transports to the tissues oxygen, absorbed from the air by the lungs; that it carries from the tissues various waste products formed in the processes of dissimilation; that it is the medium for the transmission of the internal secretion of certain glands; that it aids in equalizing the temperature and water contents of the body.

The total quantity of blood in the body has been determined approximately for man as one-thirteenth of the body weight. The specific gravity of human blood in the adult may vary from 1.041 to 1.067, the average being about 1.055.

The blood is composed of a liquid part, the plasma, in which float a vast number of microscopical bodies, the blood corpuscles, known respectively as the red corpuscles, the white corpuscles or leucocytes, of which in turn there are a great many different kinds, and the blood plates.

Blood plasma, when obtained free from corpuscles, is perfectly colorless, in thin layers, for example, in microscopical preparation; when seen in large quantities it shows a slightly yellowish tint. The red color of the blood is not due, therefore, to coloration of the blood plasma, but is caused by the mass of red corpuscles held in suspension in the liquid. The proportion by bulk of plasma to corpuscles is usually given roughly as two to one. The blood plasma is composed of two substances, blood serum and blood fibrin. You have noticed that blood, after it has escaped from the vessels, usually clots or coagulates. The clot, as it forms, gradually shrinks and squeezes out a clear liquid, to which the name blood serum has been given. Serum resembles the plasma of normal blood in general appearance, but differs from it in composition. Here it is sufficient to say that blood serum is the liquid part of the blood after coagulation has taken place. You can prepare this experiment for yourself: If shed blood is whipped vigorously with a rod or some similar object while it is clotting, the essential part of the clot, namely the fibrin, forms differently from what it does when the blood is allowed to coagulate quietly. It is deposited in shreds on the whipper. Blood that has been treated in this way is known as defibrinated blood. It consists of blood serum plus the red and white corpuscles, and as far as appearances go it resembles exactly the normal blood; it has lost, however, its power of clotting.

Red blood corpuscles are bi-concave, circular disks, without nuclei; their average diameter is 7.7 microns (1 micron equals 1–25,000 of an inch); their number, which is usually reckoned as so many to a cu. millimeter, varies greatly under different conditions of health and disease. The average number is given as 5,600,000 per cubic millimeter for males and 4,500,000 per cubic millimeter for females.

The number of red corpuscles also varies in individuals with the constitution, nutrition and manner of life. It varies with age, being greatest in the fetus and in the new-born child. It varies with the time of the day, showing a distinct diminution after meals. In the female it varies somewhat with menstruation and pregnancy, being slightly increased in the former and diminished in the latter condition.

The red color of the corpuscles is due to the presence in them of a pigment, known as hemoglobin. Owing to the minute size of the corpuscles, their color when seen singly under the microscope is a faint yellowish red, but when seen in mass they exhibit the well-known blood-red color, which varies from a scarlet in arterial blood to a purplish red in venous blood, this variation in color being dependent upon the amount of oxygen contained in the blood in combination with the hemoglobin. The function of the red blood corpuscles is to carry oxygen from the lungs to the tissues. This function is entirely dependent upon the presence of hemoglobins, which have the power of combining easily with the oxygen gas.

White blood corpuscles or leucocytes contain no hemoglobin or coloring matter. They have a nucleus or center spot. Their size varies from 5 to 12 microns, and are less numerous than the red corpuscles, being in this proportion: one white corpuscle to 500 red corpuscles. The chief functions of the white corpuscles are: (1) That they protect the body from pathogenic or disease-producing bacteria. In explanation of this action it has been suggested that they may either ingest the bacteria and thus destroy them directly, or they may form certain substances, defensive proteids, that destroy the bacteria. White corpuscles that act by ingesting the bacteria are spoken of as phagocytes (meaning to eat the cell). (2) They aid in the absorption of fats from the intestines. (3) They aid in the absorption of peptones from the intestines. (4) They take part in the process of blood coagulation. (5) They help in maintaining the normal composition of the blood plasma in proteids.

Blood plates are small circular or elliptical bodies, nearly homogeneous in structure, variable in size, always much smaller than the red blood corpuscles. Less is known of their origin, fate and functions than in the case of the other blood corpuscles, but there is some considerable evidence to show that they take part in the process of coagulation or clotting.

Coagulation of the Blood.—One of the most striking properties of the blood is its power of clotting, or coagulating, shortly after it leaves the blood-vessels, or if any foreign elements come in contact with it. The general changes in the blood during this process are easily followed. At first perfectly fluid, in a few minutes it becomes viscous, and then sets into a soft jelly, which quickly becomes firmer, so that the vessel containing it can be inverted without spilling the blood. The clot continues to grow more impact, and gradually shrinks in volume, pressing out a greater or smaller amount of clear, faintly yellow liquid, to which the name blood serum is given. The essential part of the clot is the fibrin.

Fibrin is an insoluble proteid not found in normal blood. In shed blood, and under certain conditions while still in the blood-vessels, this fibrin is formed. In forming, it shows an exceedingly fine network of delicate threads that permeate the whole mass of the blood and gives the clot its jelly-like character. The shrinking of the threads causes the subsequent contraction of the clot. If the blood has not been disturbed during the act of clotting, the red corpuscles are caught in the fine fibrin mesh-work, and as the clot shrinks these corpuscles are held more firmly, only the clear liquid of the blood being squeezed out, so it is possible to get specimens of serum containing few or no red blood corpuscles. The white corpuscles or leucocytes, on the contrary, although they are also caught at first in the forming meshes of fibrin, in latter stages of the clotting they readily pass out into the serum, on account of their power of having movement. If the blood has been agitated during the process of clotting, the delicate net work will be broken in places, and the serum will be more or less bloody—that is, it will contain numerous red blood corpuscles. If during the time of clotting the blood is vigorously whipped with a bundle of fine rods, all the fibrin is deposited as a stringy mass on the whipper, and the remaining liquid part consists of serum plus red corpuscles. Blood that has been whipped in this way is known as defibrinated blood. It resembles normal blood in appearance, but is different in composition; it can not clot again. The way in which fibrin is normally deposited can be easily demonstrated by taking a drop of blood on a slide and covering it with a cover slip, allow it to stand several minutes until coagulation is complete, and view under a microscope. If the drop is examined, it is possible by careful focusing, to discover in the spaces between the masses of corpuscles many examples of delicate fibrin net work. The physiological value of the clotting of blood in life is that it stops hemorrhages by closing the openings of the wounded blood vessels, but the clotting of the blood after death, is to the embalmer one of the bugbears, and a real method of preventing it, or of dissolving the clot after it has once formed in the blood vessels is one of those difficult problems which remains as yet unsolved.

Since we have no real method of preventing coagulation in the blood vessels, let us search out the things which will hasten or retard this coagulation. Blood coagulates normally within a few minutes after it is liberated from the blood vessel, but this process may be hastened by increasing the amount of foreign substance with which it comes in contact. Thus the agitation of the liquid in quantity or the application of a sponge or handkerchief or the application of heat hastens the onset of clotting.

Coagulation in drawn blood may be retarded or prevented altogether by a variety of means, of which the following are the most important:

(1) By cooling.

(2) By the action of neutral salts.

(3) By the action of oxalate solutions.

(4) By the action of sodium fluoride.

Summary.—To summarize then, the following statements may be made:

(1) The immediate factor necessary to the clotting of the blood is the fibrin.

(2) That blood does not clot normally in the blood vessels before death.

(3) That after death blood remains for a long time without clotting, provided some outside agent is not introduced to cause it.

Such an agent may be the blood coming in contact with the air, or the blood drainage tube. The one point then to be emphasized is that when a vein is cut, and the blood begins to flow, you know that the blood is not in a coagulated condition. Then work rapidly, put the blood drainage tube quickly into the vein and draw off as much blood as you can before it begins to clot at the end of the tube. The great trouble has been, that the embalmer does not work with precision. He first raises the vein, and exposes it on the surface of the incision. He then raises the artery. He places the drainage tube into the vein, but shuts it off till he is ready with the artery. Now, by the time he has placed the arterial tube in the artery, injected a few bulbs full to see that all is in working order, and has perhaps attended to a few other duties, he is amazed to find that the blood will not flow, that it has clotted. What is the reason? He gave it time to clot after the drainage tube was inserted.

A better procedure would be not to touch the vein until every other procedure has been attended to. Then raise the vein, insert the drainage tube and withdraw the blood quickly, and at the same time keep injecting slowly into the arterial system to keep up the needed pressure to keep the blood flowing.

(4) That when a clot is once formed in a blood vessel, it is not dissolved by the addition of fluid or any other solution.

(5) That sometimes when the blood has become clotted at the end of the drainage tube, it can be loosened up or be slightly pushed away by attaching the pump to the drainage tube and injecting a few bulbs of fluid, which, when it runs out, will again start the flow of blood.