BLOOD

red fluid which circulates in the arteries and veins of animals, in order to nourish the body, to carry away waste products to the excretory organs, and to protect the body against invading organisms. Human b. has S.G. 1.055, a salt taste, and an alkaline reaction. It is composed of the fluid element, or blood plasma, which carries food substances and waste products in solution, and the cellular elements, or red and white corpuscles and blood platelets. In a cubic millimetre of human b. there are about 5,000,000 red corpuscles, 8000 white corpuscles, and 500,000 blood platelets. In shape a red corpuscle is a disc, concave on each side, and slightly thicker at the edge. It is composed chiefly of nitrogenous material with which is in loose chemical combi globin, which combines with oxygen and yields it up on its concentration decreasing. This power of oxygen-carrying, which the red corpuscles have in the hemoglobin, is their most important quality. White corpuscles, or leucocytes, are derived from lymph glands and the spleen, and are of various kinds and shapes, being cla ified mainly according to the staining qualities they exhibit under the microscope. The great value of the white corpuscles is in the power they have of destroying inflammation products, etc., and thus protecting the body. Blood platelets are small circular bodies, about half the size of red corpuscles, and are believed to have an important function in the clotting of b. In the proce of clotting fibrin is precipitated from the plasma in the form of fine threads, which interlace in every direction, and entangle the corpuscles in their meshes; during the proce fibrin is also believed to be derived from the dumps which form blood platelets. Resistance to disease caused by bacteria is due to the white corpuscles and the formation of certain anti-bodies in the b., which either destroy the bacteria or a ist the white corpuscles to do so. This resistance can be produced or stimulated artificially by the injection of the products of bacteria or their toxins in regulated non-lethal doses. In Anzmia, either primary or secondary, the amount of hemoglobin in the blood is le ened, either in the individual red corpuscles, or through diminution in the number of red blood corpuscles. In Leucocythemia, or Leukemia, the white corpuscles are enormously in- '_ ereased, being deposited in the liver, kidney, and other organs; and there is anemia