346 HUMAN PHYSIOLOGY 



The color, which is found to be a dirty yellow when separate corpus- 

 cles are viewed under the microscope, is due to a proteid material 

 called haemoglobin. Haemoglobin, which constitutes about 35 

 per cent of the corpuscle, contains a large amount of iron. It has 

 the power of uniting very readily with oxygen whenever that 

 gas is abundant, and after having absorbed it, of giving it up to 

 the surrounding media, when oxygen is there present in smaller 

 amounts than in the corpuscle. This function of carrying oxygen is 

 the one important function of the red corpuscles. The taking 

 up of oxygen is accompanied by a change in color of the mass of 

 corpuscles from a dull red to a bright scarlet. 



Length of Life of Red Corpuscles. — It is difficult to say just 

 how long the red corpuscles live in the body. We know, how- 

 ever, that large numbers are destroyed every day. 



The coloring matter of the bile, and possibly other body excre- 

 tions, is due to the color obtained from the worn-out blood cor- 

 puscles. To make up for the loss of the red corpuscles, new ones 

 are manufactured in the red marrow of bone. The red marrow 

 cells are in a continual state of division, forming new red corpuscles 

 which at first are nucleated cells. These later lose their nuclei 

 and become disk-shaped. 



The Colorless Corpuscle ; Structure and Functions. — A colorless 

 corpuscle is a cell irregular in outline, the shape of which is con- 

 stantly changing. These corpuscles are somewhat larger than the 

 red corpuscles but less numerous, there being about one colorless 

 corpuscle to every three hundred red ones. They seem to have 

 the power of movement, for they are found not only inside blood 

 vessels, but outside the blood tubes, showing that they have worked 

 their way between the cells that form the walls of the blood 

 vessels. 



A Russian zoologist, Metchnikoff, after studying a number of 

 simple animals, such as medusse and sponges, found that in such 

 animals some of the cells lining the inside of the food cavity take 

 up or engulf minute bits of food. Later, this food is changed 

 into the protoplasm of the cell. Metchnikoff believed that the 

 colorless corpuscles of the blood have somewhat the same 

 function. This he later proved to be true. Like the amoeba. 



