206 NUTRITION AND METABOLISM 



will form maltose, or a similar sugar, isomaltose. Lipase is able to 

 produce fat from glycerin and fatty acids. A solution of albumose 

 with tr3:psin or pepsin gives a precipitate of a body which is more com- 

 plex than albumose and which gives the protein reactions. It is 

 believed by many physiologists that pepsin and rennet are the same 

 body. Under certain conditions, it has a dissolving power, under other 

 conditions it has the power to coagulate. 



The reversibility of enzymic action has given rise to much specula- 

 tion about assimilation and growth. It seems reasonable to suppose 

 that the cell forms its protoplasm from amino-acids by the reversed 

 action of proteolytic enzymes. In the same way, cellulose may be 

 formed from dextrose, fat from glycerin and fatty acids. Nearly all 

 phases of growth can be accounted for in this way. This is nothing but 

 theoretical speculation, and the only fact to support it is the reversi- 

 bility of certain enzymes. The conditions under which chemical reac- 

 tions take place inside of the cell are very largely unknown. -There 

 are so many processes going on at the same time that it is absolutely 

 impossible at the present time to obtain a perfect understanding of all 

 these reactions. Thus, o\ir knowledge of growth is largely based 

 upon analogy and speculation. 



