information as to the chemical structure of the more com- 

 plicated nitrogenous substances. The explanations now 

 given as to how this elaboration takes place are largely 

 hypothetical and must be regarded as quite unsatisfactory. 



A step further from the proteid food is the question of 

 living protoplasm itself, and one of the most interesting 

 problems connected with this is the nature and functions 

 of the enzymes, the ferments and digestive secretiojpi 

 of living cells. Many of the newer theories as to the na- 

 ture of living protoplasm hark back to investigations 

 regarding enzymes, indeed some extremists advance the 

 opinion that the activities of the live protoplast are in 

 themselves but the result of the interaction of substances 

 enzymatic in their nature. There is no doubt of the power 

 of the appropriate enzymes when present even in infini- 

 tesimal amount to cause enormous molecular changes in 

 the substances on which they act, but it is necessary to 

 exercise extreme caution before accepting generalizations 

 along this line, no matter how brilliant. The amount of 

 empirical information in this field is already becoming 

 unwieldly, and nowhere else is the necessity of unifying 

 principles so plainly shown. Here it is that more definite 

 chemical knowledge may in one stroke clear up the whole 

 situation. 



If it is not possible to ascertain the chemical structure 

 of a single enzyme, how much more difficult then must it 

 be to determine that of the living protoplasm? It goes 

 without saying, that if we try to analyze the living proto- 

 plasm, in the ordinary chemical sense, we kill it. This 

 being the case, the student who is trying to penetrate these 

 difficult problems must have recourse to other modes of 

 attack. Therefore does he experiment with the effect of 

 agents which do not kill but merely stimulate the organ- 

 ism or partially inhibit its functions and, by studying the 

 nature and products of the reactions produced, obtain 



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