26 THE VITAL PROCESSES 



about ^fotf of an inch (1.9 microns). The red corpuscles 

 are exceedingly numerous, there being as many as five 

 millions in a small drop (one cubic millimeter) of healthy 



FIG. 9. Red corpuscles from various animals. Those from mammals 

 are without nuclei, while those from birds and cold-blooded animals have 

 nuclei. 



blood. But the number varies somewhat and is greatly 

 diminished during certain forms of disease. 



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. 1 

 The performance of this function depends upon the hemo- 

 globin. 



Hemoglobin. This substance has the remarkable property of form- 

 ing, under certain conditions, a weak chemical union with oxygen and, 

 when the conditions are reversed, of separating from it. It forms 



1 The peculiar shape of the red corpuscle has no doubt some relation to its 

 work. Its circular form is of advantage in getting through the small blood vessels, 

 while its extreme thinness brings all of its contents very near the surface a con- 

 dition which aids the hemoglobin in taking up oxygen. If the corpuscles were 

 spherical in shape, some of the hemoglobin could not, on account of the distance 

 from the surface, so readily unite with the oxygen. 



