222 HUMAN PHYSIOLOGY 



organism. The largest are found in small reptilian 

 or amphibian forms, the smallest in mammals of good 

 size. In general, the corpuscles of the warm-blooded are 

 smaller than those of the cold-blooded types. This 

 appears meaningless until the function of the corpuscles 

 is stated. Their particular service is to absorb, carry, 

 and deliver oxygen. For such a purpose small cor- 

 puscles in great numbers must be superior to large cor- 

 puscles in smaller numbers. The characteristic of 

 the warm-blooded animal is the high oxygen requirement. 

 Moreover, if the corpuscles are small, the network of 

 vessels through which they are sent can be finely divided 

 and bring them close to all the cells to which they are to 

 minister. 



It is the total surface of the red corpuscles which counts 

 in the execution of their specific function. As a result of 

 their vast number and their shape the aggregate surface 

 is well nigh incredible. Calculations have placed it as 

 high as % acre for one human being. An able 

 writer has made this area easy to visualize by saying 

 that it equals four baseball diamonds. This does not 

 mean that four diamonds could be covered by the cor- 

 puscles from the blood of one man for we are reckoning 

 both sides and allowing for the edges. Still, it is prob- 

 able that the corpuscles would make a continuous film 

 over a plot of ground 100 feet square. It would be 

 too delicate to redden the surface or to be apparent in 

 any way. 



The chief solid in the red corpuscles is called hemo- 

 globin. This is a protein and of unusual complexity 

 even for a representative of that class of compounds. In 

 addition to the five elements we expect to find in proteins 

 generally (carbon, oxygen, nitrogen, hydrogen, and 

 sulphur) the red pigment of the blood is exceptional in 

 containing iron. The percentage is low but there is 

 iron enough in the blood of a man to make a small nail. 

 The popular notion according to which iron and "good 

 red blood" are connected has some basis in fact. 



