The solution prepared from the hydrocele fluid causes blood serum to coagulate; that prepared from the blood serum causes the hydrocele fluid to coagulate; and when mixed together the mixture of the two solutions coagulates; while the serum and hydrocele fluid from which the substances have been removed no longer have the power of exciting coagulation in each other or in like fluids. Here, then, are two materials; one, obtained in considerable quantity from serum after coagulation, is called paraglobulin (Schmidt) or serum globulin (Hammarsten); the other, occurring in serous fluids, is named fibrinogen. Both these substances are present in the dying plasma of the blood prior to coagulation. They can be obtained both together from the plasma if the plasma be treated with sodium chloride to saturation after either of the precautions already mentioned-viz., the application of cold, or the addition of neutral salt-has been taken to prevent the formation of fibrin. This precipitates a substance which readily dissolves if water be added to weaken the salt solution, and after some time the solution undergoes spontaneous coagulation, while the plasma from which it has been made has lost that power. This plasmin (Denis) no doubt is made up of different globulins, chiefly serum globulin, and fibrinogen, and contains in itself all the necessary "factors" of fibrin formation, but is not at all identical with fibrin, since it readily dissolves in weak saline solutions, like the class of proteids called globulins, while fibrin is quite insoluble in such solutions.

In plasma removed from its normal relationships, both serum globulin and fibrinogen exist; but the former in far greater quantity than the latter, since the serum, after the blood clot is formed, contains no more fibrinogen, while the serum globulin makes up nearly half the remaining solids.

In preparing fibrinogen and serum globulin Schmidt found that the more carefully he operated, the weaker and more uncertain their action as fibrin factors became; and, finally, he made solutions which, when added together, did not produce coagulation, but which, when added to less pure solutions, gave good, firm clots. From this he suspected that a third agent which acted as a ferment was necessary to put into operation the

fibrin-producing properties of the other two factors. He further succeeded in preparing the third agent, to which he gave the name of fibrin ferment. By treating serum with strong alcohol the proteids are precipitated; the ferment is carried down with them, and extracted with water. This extract, added to the mixture of the pure fibrin factors, which previously did not clot, caused rapid coagulation, but not when added to either of them singly.

This material is influenced by those circumstances which affect the activity of ferments in general: it has a minimum, 0° C., optimum, 38° C., and maximum, 80° C., temperature of activity, with various gradations of rapidity of action between each, and is destroyed if heated above 80° C. An active solution having the properties of the ferment can be extracted from whipped fibrin preserved in alcohol by an 8 per cent. solution of common salt (Gamgee).

Hammarsten thinks that the serum globulin is not indispensable to the formation of fibrin, because (1) a solution of fibrinogen may be made to coagulate without its presence; (2) the fibrinoplastic property of serum globulin is shared by casein and calcic chloride; (3) and is absent from pure serum globulin, (4) such as is present in hydrocele fluid which does not coagulate on the addition of fibrin ferment.

The source of fibrin is still a question of much difficulty, and will be further discussed with the question of blood coagulation within and without the vessels, after the morphological elements have been described.

FIBRIN.

Fibrin may be procured either from plasma or blood by whipping, and then washing the insoluble product with water. When fresh it has a pale yellow or whitish color, a filamentous structure, and is singularly elastic. It is not soluble in water, weak saline solution, or ether. Alcohol makes it shrink by removing its water. When quite dry it is brittle and hard, and can be reduced to a powder. It swells in 1 per cent. hydrochloric acid, and if warmed is converted into acid albumin and dissolved.

The amount formed varies very much even in the blood drawn

from the same animal at the same time, but is always very small compared with the size of the blood clot. It never reaches as much as 1 per cent., commonly varying from 0.1 per cent. to 0.3 per cent. of the entire mass of blood.

SERUM.

This name is given to the clear fluid which oozes out of the clot of plasma. It only differs from the latter in its chemical composition in so far that fibrin is separated from it. Though chemically this is a slight difference, it signifies the change from a complex living body (blood plasma) into a solution of dead albumins, etc.

Serum is a clear, straw-colored, alkaline fluid of 1028-1030 sp. gr., holding in solution different organic substances and some inorganic salts. After a full meal the serum is said to be slightly milky, from the presence of finely divided fat.

It contains about 9 per cent. of solid matters, of which a large proportion, 7 per cent., are proteids. Of these the most abundant is (1) serum albumin (about 4 per cent. in man), a solution of which becomes opaque at 60° C., and coagulates at a heat of 73° -75° C. The proteid next in importance is (2) serum globulin or paraglobulin (about 3 per cent. in man), which has already been mentioned. It may be precipitated imperfectly by CO., or completely by magnesium sulphate. (3) Serum casein has been obtained from serum by careful neutralization with acetic acid after the removal of the serum globulin by CO,. This is said to be serum globulin which has failed to come down with the CO2. (4) Neutral fats in a state of fine subdivision are present in a variable quantity: also (5) lecithin; (6) traces of sugar; (7) various products of tissue change-kreatin, urea, etc.; and (8) inorganic salts, viz., sodium chloride, about 5 per cent., and sodium carbonate, which probably existed in the blood as sodium hydric carbonate. There is also a small quantity of potassium chloride. But it should be remembered that about ten times more sodium than potassium salts exist in the serum, and probably in the blood plasma.

CHAPTER XIV.

BLOOD CORPUSCLES.

The relative number of red discs to the colorless cells is said

to be, on the average, 350 to 1.

This is true of the blood drawn from the fine vessels by puncture. While in the vessels the blood must contain a greater proportion of the colorless cells, for by the ordinary method of obtaining blood for examination, they do not flow out of the punc

tured capillaries as readily as the red discs, and many of them are said to become dis

integrated very shortly after they are removed from the circulation. Although the number of red discs normally alters but little, on account of the constant changes occurring in the number of the white cells, the proportion of white to red varies much. It has been found to differ according to the observer, the situation, and other circumstances, as shown in the following table, which gives the number of red corpuscles to one colorless cell :

Observer's estimate of normal proportion :

Welcker........

Moleschott............ ......

In various parts of the circulation :-

Red. White.

335-1

357-1

In a disease of the spleen and lymphatic glands called Leucocythemia there may appear to be nearly as many white cells as red discs. Here, however, the red discs are deficient, while the colorless cells are multiplied.

THE COLORLESS CORPUSCLES.

The colorless cells of the blood, commonly called the white corpuscles, differ in no essential respect from the pale round cells which are found in most of the tissues of the body. They exist in large numbers in that fluid, namely, the lymph, which is drained back from the tissues into the blood, and occupy a great part of the lymphatic glands and spleen. They are often spoken of as lymphoid cells, leucocytes, indifferent, or formative cells, on account of their being so widely distributed throughout the tissues.

When fresh blood is examined with the microscope these cells can generally be seen adhering to the glass slide or cover glass and lying singly, apart from the groups of red discs. They can be recognized by their absence of marked color, finely granular structure, spherical shape, and the nuclei which may often be recognized near the centre of the cell. Though not always visible in fresh preparations, the nuclei can be brought to light by the action of many reagents-e. g., acetic acid. If examined while being moved by the blood current in the capillary vessels, they are seen to pass slowly along in contact with the vessel wall, while the red corpuscles rush rapidly past them down the centre of the channel (Fig. 98). This may partly be due to their peculiar adhesiveness, which also causes them to stick to the glass slide, while the red discs are washed away when a gentle stream of saline solution is allowed to flow under the cover glass. These cells show all the manifestations of activity characteristic of independent living beings. If kept in a medium suitable to them, and at the temperature of the body, they will soon be seen