22 Living and Dead Matter and 



areas the nature of the first settler is determined 

 chiefly by the carrying power of wind (or waves and 

 birds) . 



We may now return from this digression to the real 

 object of our discussion, namely that the nutritive 

 solutions of organisms must be very dilute and consist 

 of the split products of the complicated compounds 

 of which the organisms consist. The examples given 

 sufficiently illustrate this statement. 



The nutritive medium of our body cells is the blood, 

 and while we take up as food the complicated com- 

 pounds of plants or animals, these substances undergo 

 a digestion, i. e., a splitting up into small constituents 

 before they can diffuse from the intestine into the blood. 

 Thus the proteins are digested down to the amino 

 acids and these diffuse into the blood as demonstrated 

 by Folin and by Van Slyke. From here the cells take 

 them up. The different proteins differ in regard to 

 the different types of amino acids which they contain. 

 While the bacteria and fungi and apparently the higher 

 plants can build up all their different amino acids from 

 ammonia, this power is no longer found in the mammals 

 which can form only certain amino acids in their body 

 and must receive the others through their food. As 

 a consequence it is usually necessary to feed young 

 animals on more than one protein in order to make 

 them grow, since one protein, as a rule, does not contain 

 all the amino acids needed for the manufacture of all 



