462 LECTURE XX. 



ing their constitution; in fact, we do not even know to what class of com- 

 pounds they belong, or whether they form a class of their own. It has 

 always been customary to classify the ferments with the proteins. There 

 were various reasons for this assumption. .Until recently, the composition 

 and structure of the proteins were as little understood as that of the fer- 

 ments themselves, while the fats and carbohydrates had been thoroughly 

 investigated. Our knowledge concerning the compositions of the latter 

 compounds makes it seem improbable that the ferments belong to either 

 of these two classes. The proteins, on the other hand, with their compli- 

 cated structure and their various elementary components, are far more 

 likely to include the ferments, endowed as they are with such numerous 

 and finely differentiated functions. We are, however, at present unable 

 with our limited knowledge of the proteins to draw any conclusions regard- 

 ing the structure of the ferments. It is often stated, in order to show their 

 albuminous nature, that the pure ferments give the reactions of the proteins. 

 Unfortunately, we have not yet succeeded in isolating any ferment in a 

 pure state. In the first place, we have absolutely no criterion of purity. 

 Pekelharing 1 and M. Nencki and N. Sieber 2 have recently attempted to 

 purify the pepsin of the stomach, the former claiming to have accomplished 

 the feat. Until we have some clear conception of the composition of the 

 ferments, it is of little avail to discuss their nature. We are not even jus- 

 tified in assuming that the ferments belong to a single class of compounds. 

 It is possible that the fats and carbohydrates also take part in their com- 

 position. For the present we are unable to state that the identification 

 of this or that compound actually indicates that it belongs to the ferment. 

 Such substance may simply be dragged down mechanically in the process 

 of isolating the ferment. All of our methods for the preparation of the 

 ferments are such that this assumption is justified. 



The ferments are unquestionably closely related to the life-processes of 

 the cells. They are to be directly looked upon as their secretion products. 

 The ferments, until recently, were sharply divided into two groups, the 

 organized ferments, or simply ferments, and the unorganized ferments, or 

 enzymes. Those which were only active in the presence of the living cell 

 were included with the former, while those which acted independently 

 of the cells, such as diastase, pepsin, trypsin, etc., were placed in the 

 latter class. The designation organized or unorganized, was to give the 

 impression that, in the first case, the protoplasm of the cell was absolutely 

 necessary for performing the function of the ferment, while the unorgan- 

 ized ferments were capable of accomplishing their work without any 

 further assistance. It is true, however, that we are not at all acquainted 



1 Z. physiol. Chem. 22, 233 (1896/97); 36, 8 (1902). 

 3 Ibid. 32, 291 (1901). 



