70 VITALISM AND SCHOLASTICISM 



it, is an increase in size always, however, within 

 certain limits peculiar to each species, very 

 wide limits in some cases but still definite 

 limits, so that one can always say of any given 

 species that it will not exceed a certain size 

 or fall below a given limit. 



Respiration Respiration is a process closely associated 

 with those which we have been considering. 

 This consists essentially in the elimination of 

 the superfluous carbon dioxide produced by 

 the operations of the body and the introduction 

 of oxygen by which the carrying on of further 

 such processes is rendered possible. Thus in 

 the human being where, as in all creatures with 

 red blood-corpuscles, the process is carried on 

 by those cells, the expired air contains about 

 3.5 per cent, of carbon dioxide and 17 per cent, 

 of oxygen, the former being about 3.2 per cent, 

 more and the latter 4.0 per cent, less than the 

 amount contained in the inspired air. We 

 cannot see the process of respiration taking 

 place in the amoeba but we must suppose that 

 the interchange of gases which constitutes this 

 process takes place all over the surface of the 

 creature. 



But if we cannot see the respiration taking 

 place there is one further very remarkable 

 phenomenon which we can study and that is 

 the process of reproduction. In the amoeba 



