Fig. 9—Red corpuscles from various animals. Those from mammals are without nuclei, while those from birds and cold-blooded animals have nuclei.
It is the function of the red corpuscles to serve as oxygen carriers for the cells. They take up oxygen at the lungs and release it at the cells in the different tissues.[8] The performance of this function depends upon the hemoglobin.
Hemoglobin.—This substance has the remarkable property of forming, under certain conditions, a weak chemical union with oxygen and, when the conditions are reversed, of separating from it. It forms[pg 027] about nine tenths of the solid matter of the red corpuscles and to it is due the colors of the blood. When united with the oxygen it forms a compound, called oxyhemoglobin, which has a bright red color; the hemoglobin alone has a dark red color. These colors are the same as those of the blood as it takes on and gives off oxygen. The stroma, which forms only about one tenth of the solid matter of the corpuscles, serves as a contrivance for holding the hemoglobin. The conditions which cause the hemoglobin to unite with oxygen in the lungs and to separate from it in the tissues, will be considered later (Chapter VIII).
Disappearance and Origin of Red Corpuscles.—The red corpuscles, being cells without nuclei, are necessarily short-lived. It has been estimated that during a period of one to two months, all the red corpuscles in the body at a given time will have disappeared and their places taken by new ones. The origin of new corpuscles, however, and the manner of ridding the blood of old ones are problems that are not as yet fully solved. The removal of the products of broken down corpuscles is supposed to take place both in the liver and in the spleen.[9]
Regarding the origin of the red corpuscles, the evidence now seems conclusive that large numbers of them are formed in the red marrow of the bones. The red marrow is located in what is known as the spongy substance of the bones (Chapter XIV) and consists, to a large extent, of cells somewhat like the red corpuscles, but differing from them in having nuclei. These appear to be constantly in a state of reproduction. The blood, flowing through the minute cavities containing these cells, carries those that have been loosened out into the blood stream. Nuclei appear in the red corpuscles at the time of their formation, but these quickly separate and, according to some authorities, form the blood platelets.
White Corpuscles.—The white corpuscles, or leucocytes, are cells of a general spherical shape, each containing one, two, or more nuclei. They are much less numerous than the red, there being on the average only one white [pg 028]corpuscle to about every five hundred of the red ones. On the other hand, the white corpuscles are larger than the red, one of the former being equal in volume to about three of the latter.
Fig. 10—Escape of white corpuscles from a small blood vessel (Hall). At A the conditions are normal, but at B some excitation in the surrounding tissue leads to a migration of corpuscles. 1, 2, and 3 show different stages of the passage.
The white corpuscles are found, when studied under favorable conditions, to possess the power of changing their shape and, by this means, of moving from place to place. This property enables them to penetrate the walls of capillaries and to pass with the lymph in between the cells of the tissues. The white corpuscles are, therefore, not confined to the blood vessels, as are the red corpuscles, but migrate through the intercellular spaces (Fig. 10). If any part of the body becomes inflamed, the white corpuscles collect there in large numbers; and, on breaking down, they form most of the white portion of the sore, called the pus.