368 



THE BLOOD AND ITS CIRCULATION 



material called haemoglobin. Haemoglobin 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 most important function of the red corpuscle, 

 although the red corpuscle also removes part of the carbon dioxide 

 from the tissues on their return to the lungs. 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. 



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 have the power of movement, 



Diagram showing how the colorless corpuscles 

 pass through the walls of the capillaries 

 (smallest blood tubes) and ingulf the bacteria 

 at m. 



A colorless corpuscle catching 

 and eating a germ. 



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, Metschnikoff, after studying a number of 

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

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

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

 the protoplasm of the cell. Metschnikoff believed that the colorless 



