64 HUMAN PHYSIOLOGY 



with to the tissues ; for in the absence of oxygen no 

 vital action can be performed and no other food 

 utilised. We thus discover that the great function 

 of the red blood corpuscles is that of acting as the 

 oxygen carriers of the blood, so that this gas may be 

 perpetually conveyed to every tissue of the body. 

 The red blood corpuscles discharge yet another duty. 

 It has been shown that the blood gathers waste 

 material from the tissues, this waste representing the 

 result of bodily wear and tear. A part of this waste 

 consists of carbonic acid gas, which, conveyed to the 

 lungs, is breathed out. The red blood corpuscles are 

 also carriers of carbonic acid gas to the lungs, so 

 that if on the one hand they act as distributors of 

 food in the shape of oxygen, on the other they 

 serve as scavengers for the removal of waste. The 

 difference in colour between the light red of pure or 

 arterial blood and the darker colour of impure or 

 venous blood, is explained by the fact that when car- 

 bonic acid gas unites with the haemoglobin a darker 

 hue is produced. 



Fig. 19. A WHITE BLOOD CORPUSCLE OF MAN 



SHOWING HOW IT ALTERS ITS SHAPE. 



THE WHITE CORPUSCLES. The white corpuscles 

 are microscopic bodies of very different nature from 

 the red. Each white blood corpuscle is in fact a 

 living cell, and as such, possesses a kind of semi- 

 independent existence in the blood in which it lives. 

 Studied under special conditions by the microscope, 

 a white blood corpuscle is seen to move through the 



