further oxidation become fibrin, and the cells bursting may allow the particles to assume the thread-like form. This would suggest that coagulation is attended by, or may be due to oxidation—a view which the necessity for free exposure to air strengthens. The coagulation of albumen by nitric acid may be also due to oxygen, which that substance so readily affords, converting it into an amorphous form of fibrin. There are most white cells between the opening of the thoracic duct and the lungs, where oxidation gives rise to fibrin. In inflammatory blood there is often a layer of white cells between the red clot and the buffy coat, where they cannot be exposed to the action of the air. Virchow states that fibrin as such is never an exudation from the blood, which, however, contains matter readily convertible into it by local causes. Inflammation of parts freely supplied with lymphatic vessels and glands, as lung, pleura, liver, &c., is a most fruitful source of increase of fibrin, whereas phrenitis scarcely alters the amount, and it is known the brain possesses few if any lymphatics. He also has shown that lymph-fibrin differs from blood-fibrin in never coagulating within the vessels, as it has not as yet met with air; it does so when exposed to the atmosphere. Denis and Lecanu, from chemical considerations, support the view that the cells contain fibrin. Carpenter believes that the white cells develop fibrin, or convert other albuminoids into it; and there is scarcely any fibrin in the chyle in its earlier stages of development, or till it is passed through the mesenteric glands, where the white cells are known to be generated.

The point we are now discussing involves the question "whether is fibrin or albumen the higher in the scale of organization ?" and we shall briefly state the arguments which have been advanced on either side. Zimmerman

first started and Simon ably supported the doctrine, that fibrin was merely effete matter, as it exists in such small proportion to the albumen, and it is nearly absent from

portal blood, which we know must carry back the nutrient matter which results from digestion. Hepatic venous blood contains it more abundantly. Its amount is proportionally increased in anemia, exhausted states of the system-where the waste has exceeded the supplyby starvation, and after bleeding. Andral and Gavarret showed that improvement in the breed of animals diminished its proportion. Moreover, there is little or none in fœtal blood, that of carnivora, chyme, or in the egg, which of course are highly nutritive. The property of fibrillation is very analogous to gelatinization, as fibrin first forms a jelly-like mass out of which fibrils develop, and to which it can be again reduced artificially or within the body, as we see in aneurismal clots. Mucus also, a substance acknowledged to be in a state of regression, has similar jelly-like and fibrillous stages. Liebig says fibrin may be " perhaps albumen, half converted into gelatin." Its existence in very small quantity in the blood of ceruleans supports the same view, as in these individuals, like cold-blooded animals, there is but little waste. Fibrin is more easily converted than albumen into urea by Bechamp's method. According to the theory now propounded, the gradation would be albumen, syntonin, fibrin, gelatin, urea. On the other hand, the excess of fibrin in arterial blood, that substance having more nitrogen than albumen, according to Dumas, and the fact that 2 or 3 per 1,000 is found permanently in the blood, whereas urea, creatin, and other effete matters are at once removed, convince some physiologists that fibrin is the true nutrient pabulum of the tissues. question is far from settled. We shall return to it when treating of blood diseases.

The

III. The chemical composition of many substances in the blood has been before alluded to. We shall therefore in this place merely state the proportions they exist in, and their most important relations. The following table, arranged from the analyses of Lehmann, exhibits

the composition of blood, and separately of the cells and plasma, from a healthy man aged 25. Its specific gravity was 1.060, and it contained 513-02 parts of cells to 486.98 of plasma :

Water.....

Hæmatin (including

Hæmato-crystallin .. 127.54

7.70

7.70

127.54

The Water must vary hourly with the state of the skin and kidney and the hygrometric condition of the atmosphere; yet very surprising uniformity is maintained, as Bence Jones showed, by keeping one dog without water and the other drinking freely for months; still the blood of both was of the same specific gravity. Venesection increases the relative quantity of water, but has no power to reduce fibrin or to prevent exudation in inflammation-hence the low estimate of its value now entertained: that last drawn has the lowest specific gravity, the serous fluid of the tissues being sucked up. There is more water in women's than in men's blood.

The Albumen gives greater viscidity to the fluid, and by its very low diffusive power prevents exudation. Becquerel and Rodier state that dropsy occurs when its

proportion is less than 6 per cent. It does not impair the diffusion of substances mixed with it in the blood, for the common salt, urea, and sugar pass through animal membrane as freely as if they were dissolved in pure water. Albumen is kept dissolved by union with soda, or the tribasic phosphate of soda, which also dissolves phosphate of lime and gives the alkaline reaction to the blood.

The Fibrin is generally counted with the white cells, as they cannot be separated. There is more in arterial than in venous blood, as the oxygen in the former produces it from albumen. The blood of the porta has very little fibrin.

The Fats are olein, margarin, cerebrin, cholesterin, and serolin, which was believed to be a peculiar fat, but it is lately stated to be but a mixture of common fat and albumen. The odour of blood is said to be due to a peculiar volatile fatty acid.

As regards the mineral components, they are shown in due proportion in the preceding table, and it will be seen that the cells contain much more phosphorus and potash than the plasma, and thus seem destined for the nervous and muscular tissues.

The Gases in the blood are oxygen, nitrogen, and carbonic acid, and it will absorb from 10 to 13 volumes of the former, irrespective of sea-level.

It will be understood that the blood is ever changing its composition, containing materials in a state of formation, maturity, and decay. "They are mixed together, past, present, and future-the blood of yesterday, the blood of to-day, and the blood of to-morrow-and we have no method of separating them."

Electric properties were assigned to the blood by Dutrochet, who even stated that he could form muscular fibre from albumen by galvanism-assertions, however, disproved. Electricity reddens venous blood, as also do most neutral salts, especially those that afford oxygen.

Arterial and Venous Bloods differ materially, unless the aeration of the arterial has been interfered with, as in hot countries, under the influence of chloroform, ether, or opium; when blood has been kept delayed in the vessels, as by a tourniquet, or when it flows from a deep wound; under all these circumstances, both that from artery and vein are dark-colored. On the contrary, venous blood coming from a gland in action, as the kidney or the parotid, has been shown to be scarlet, but of the ordinary hue when no secretion is occurring. The reverse is the case in the blood coming from a muscle, which, if contracting, sends out dark blood; if at repose, sends out the arterial blood unchanged in colour. These effects are due to the production of carbonic acid. The main differences are here tabulated:

ARTERIAL.

Scarlet, not dichromatic.

Temperature, about 100°

Denser, and hence greater capacity for heat.

More fibrin and red cells.

VENOUS.

Modena or purple, but green,
in very thin layers, being di-
chromatic.

Temperature, about 98°
Lower specific gravity.

More albumen.

IV. Vital properties.-We have seen that blood within the vessels consisted of cells floating in the plasma, or liquor sanguinis; when, however, it is withdrawn, another arrangement takes place, the fibrin leaving the plasma and uniting with the cells to form a solid mass. This phenomenon is called coagulation, and was first accurately described by Harvey. The solid mass is termed crassamentum or clot; the fluid, serum, which still contains albumen; and if this be removed, the fluid is termed serosity. Coagulation then produces a rough, spontaneous analysis, as shown by the following table: