466 LECTURE XX. 



an inactive form, both in the animal and the vegetable organisms. The 

 cell is thus enabled to regulate its entire metabolism. It only activates 

 the ferments when it needs them. The way this activating process is 

 brought about is still unknown. We can imagine that the activating agent 

 splits the zymogen, perhaps forming a smaller molecule, or possibly it 

 breaks open an anhydride or lactone formation, thus permitting those 

 groups to act which are able to force an entrance into the material to be 

 acted upon. 



Although the discovery of the wide distribution of ferments and their 

 action, and the knowledge that the cell-functions in a narrow sense 

 correspond to such processes, opens up new paths and points of view for 

 Biology, although on the other hand we must not forget that the great 

 mystery of cell-life remains unsolved. The living cell produces the fer- 

 ment; of this there is no doubt. At this point we encounter the most 

 important problems of the whole subject of biology. We should be mak- 

 ing a great mistake if we were to say that the knowledge of fermen- 

 tation reactions has solved the mystery of life. It has, to be sure, cleared 

 up many processes which were previously obscure, and has given us a 

 very much clearer conception of the whole subject of metabolism. If, 

 however, we turn from fermentation to the ferments themselves, we imme- 

 diately touch the unknown. The ferments point to the cells and their 

 metabolism and functions. It would be equally short-sighted, and lead to 

 a complete misunderstanding of biological chemistry, if we were to consider 

 a solution of this mystery as impossible, and content ourselves with an 

 undefinable conception of " the vital force." There can be no doubt that 

 the rapidly advancing biological science will attack the problem of the 

 chemistry of the ferments as soon as the time is ripe. The mystery of 

 the ferments will disappear as soon as we are able to replace our conception 

 with a chemical representation. In the attempt to explain biological 

 processes more and more in accordance with the laws governing the exact 

 sciences, it is never advisable to wipe away the boundary between the 

 knowledge gained by exact methods and what has been established by 

 mere hypotheses. The more sharply we separate the known from the 

 unknown, the freer will be the development of our further investi- 

 gations, and the more independently will the facts, as such, speak for 

 themselves. 



Let us review what we know about the nature of fermentation from this 

 point of view. As a result of our unfamiliarity with the chemical nature 

 of the ferments, we are deprived of one of the most important supports 

 in any exact study concerning them, and are temporarily restricted to 

 hypotheses in explaining their manner of action. The number of ferments 

 is very large. We can here only refer to such as are in harmony with experi- 

 mental facts. 



