THE PROTEOLYTIC MECHANISM IN OPERATION 89 



a fraction of the oxygen that the red corpuscles can carry, as 

 proved by the fact that protein metabolism is unchanged when 

 the corpuscles are artificially reduced in number by thirty per 

 cent. 



The new physiological studies which suggest that air may be 

 breathed over and over without detriment that, in short, the 

 "fresh air" fetich is founded on a misconception of the needs of 

 the organism is of peculiar interest in this connection. 



In any event, it would not seem to have been necessary to 

 build a cell of an intricate type of protein merely to carry oxygen. 

 Nor is it clear why the substance of the red corpuscle should 

 contain nucleo-protein were it merely an oxygen-carrier. 



But there was need of a cell carrying a molecule of intricate 

 structure, in which might be stored the potentialities of an in- 

 finite number of atomic recombinations having their tangible rep- 

 resentation in the output of endless series of enzymes calculated 

 to carry the hydrolysis of proteins to its ultimate stages ; as also 

 to prove antidotal to an unending series of toxic by-products of 

 protein metabolism in the living or dead tissues of the number- 

 less species of animals and plants and micro-organisms with 

 which the environment teems. 



In the evolutionary history of the race, these needs have in- 

 creased pari passu with the increasing activities of the individual 

 organism, and the correspondingly varied character of the en- 

 vironment contact. And so we find, as we come up the animal 

 scale, that the red blood corpuscles constantly increase in rela- 

 tive number in the blood stream. In fishes the red corpuscles 

 form about twenty per cent, of the total volume of the blood ; 

 in frogs about twenty-five per cent.; with mammals it rises to 

 from forty to fifty per cent., and the proportion of red cor- 

 puscles to leucocytes rises in something like the same proportion. 



The primitive and generalized leucocyte retains from first to 

 last the same appearance and, as I believe, fulfills the same prim- 

 itive functions. It is a wandering phagocyte in the vascular 

 system of the sponge ; it remains a wandering phagocyte in the 

 vascular system of man. 



In the primordial state the red cell was relatively large and 

 nucleated as it still is in the embryonic state, and in certain 

 reversional diseased conditions. 



But in the developed condition the reproduction of the cor- 

 puscles devolves upon the mother cells in the red bone marrow 

 so the corpuscle itself needs no nucleus or perhaps we should 

 rather say that it is all nucleus, since it contains nucleic acids. 

 It is decreased in size, giving it relative increase of surface, 

 that it may more effectively patrol its environment ; and it is sent 

 forth from the mother cells in such galaxies that, under normal 



