BLOOD, the nutritive fluid of the tissues. consists of a transparent colorless fluid, the liquor sanguinis, and minute solid bodies, the " corpuscles " which float in it. The liquor sanguinis consists of water, in which are dissolved fibrine, albumen, chlorides of sodium and potassium, phosphates of soda, lime, and magnesia, together with fatty and extractive matters, the latter the product of the metamorphosis of the tissues. The corpuscles are of two kinds—white and red ; the white are larger and less numerous than the red, being in healthy blood in the proportion of 2 or 3 to 1000. In certain forms of disease the number of these white blood-corpuscles is increased. They present a granular appearance on the surface, have a nucleolcus, which is speedily brought into view by the action of dilute acetic acid, and aro identical with the lymph-corpuscle, Under the microscope they vary their forms in the same way as the Amoeba (see Pisti l-Ens); hence these movements are called amahoid. The rod corpuscles are peculiar to vertebrates, and seem to have their origin in the white corpfiscles, are ()Val and nucleated. M fishes, reptiles, and birds, but in man and the mammalia generally they are non nucleated, and are biconcave flattened discs, their edges being thicker than the center, hence the dark appearance of the latter when seen under the microscope. They have a great tendency to turn on their side and run into rouleaux, like 'piles of coins. Their color is straw-yellow, and it is only when seen en' masse that they give the blood its characteristic red color. The size of the human red blood-corpuscles is of an inch. They are largest in reptiles, those of the Proteus (q.v.) being of an inch in their long diameter. Hoppe Sayler has shown that, chemically, they consist chiefly of he,mo globin, with traces of albumen, cholestriu, protagcn, phosphate of potash, but no fat. The specific gravity of 13. is 1052 to 1057, and its mean quantity in an adult MAD about 344 lbs. On evaporation as a whole, the B. yields 700 parts in 1000 of water, and 210 of solid residue, which residue has nearly the same ultimate chemical composition ne that of flesh. When 13. is set aside for a time, oecasionally crystals consisting of glo bulin tinted with coloring matter appear. "The B. crystals of man and the carnivora have a prismatic form, whilst those of the rat and mouse are tetrahedral, and those of the squirrel hexagonal" (Carpenter).
Coagulation of the Blood.—When B. is drawn from the vessels, the liquor sanguinis separates into two parts—into fibrine, which becomes solid, and'a pale yellowish colored liquid, scrum. The fibrine coagulates, and in doing so entangles tho corpuscles, and forms a red mass, the clot (crassamentum). Fibrins does not exist in the 13, as iamb, but
when it appears as a coagulum in the fluid, it is produced then and there by the union of two substances present in the blood, which separate as a solid matter (Schniidt)--the one, globulin, is contained in the the other, fibrinogen, in the blood plasma, the two uniting to form the fiber of the clot. The rapidity with which this change takes place varies with circumstances. Moderate heat, and exposure to the Ai; favor it; cold and exclusion from the air retard it. The B. remains fluid in the veins for some time after death. In glanders and some forms of malignant fever, and where the B. is poor, as in scurvy, it may remain fluid. The size and firmness of the clot depends on the amount of fibrine in the B., which in health averages about 2 parts in 1000. In inflammations it is much increased, and the II. forins slowly into a tough clot, which is almost destitute of red globules on its surface, and drawn in towards the cen tor. This colorless layer is termed the &illy coat, and the physicians of bygone times used to attach great importance to it, believing that it was a phenomenon peculiar to inflammation, and bled repeatedly, with the view to its removal; whereas anything which delays coagulation, great poverty of 13., as in chlorosis (q.v.), or any condition in which the fibrine 13 in greater proportion than the red blood globules, will cause thie appearance; the clot of the impoverished blood will, however, be small and loose, and floating in an excessive quantity of scrum. The color of the 13. varies. In the arteries; it is of a bright-scarlet color, while in the veins it is of a dark-purple color. The chief difference between arterial and venous blood is that the former contains more oxygen Er5A less carbonic acid than the latter. See OF T111:1 BLOOD. This change • probably arises from the oxygen contracting the corpuscles, and altering their reflecting surfaces; carbonic acid, on the other hand, rendering them thinner and more flacciol. The changes in color can be effected in B. drawn out of the body by the application crf the gases mentioned.
The red blood-corpuscles possess great powers of absorbing oxygen. They receive oxygen in the lungs, where they become colored, and carry it all over the body to the tissues to form new combinations. After a thne, the corpuscles become dissolved in the liquor sanguinis, which fluid they serve to elaborate. The products of the metamor phosis of the tissues are poured into the B., so that it is really a very complex fluid.
See RESFIRATION,