CHANGES IN FERMENTATION. 623 



with the other direct vital actions of the micro-organisms, The fermenta- 

 that we must of necessity look on the fermentation as a physiological 



physiological function of the living cells. act of living 



L v organisms. 



We must further assume that the mode in which 

 fermentescible substances are split up differs very much 

 according to the species of micro-organism which excites 

 it. It is true that the former view, that one organism 

 exclusively possesses the power of setting up a definite 

 fermentation, is not confirmed by more recent investiga- 

 tions, but the functional action of the individual fungi 

 which set up fermentation is none the less a specific 

 one, and the same fungus always splits up the same 

 material in the same manner. This specific property Specific 



1 . /, ., -, fermentative 



also remains constant for the same species, and is activity of the 



developed whenever the other conditions suitable for 



the fermentation in question, such as material, tempera- bacteria. 



ture, &c., are present. It is only as the result of Constancy of 



certain noxious influences which will be discussed under 



the conditions of death of the lower fungi that there can 



be a loss or a weakening of this property of exciting 



fermentation. (Facts of this kind have, at any rate, Weakening of 



been observed by Fitz in the case of two butyric acid offsetting' 3 '' 



fungi.) But these attenuated bacteria cannot occasion fermentation. 



some other fermentation ; on the contrary, they retain 



their specific character, and they have only lost, as the 



result of noxious influences, that peculiar specific physio- 



logical function which is expressed in the excitation of 



fermentation. 



Although it is thus clear that we must look on 

 the fermentations as the physiological functional acts 

 of certain micro-organisms, there still remains great 

 uncertainty with regard to the mode in which we should 

 define this function, and with regard to its relation to 

 the other vital actions of the organisms. 



In the organisms which are capable of setting up The tissue 

 fermentation tissue change can run its course in various na e . ^S 1 ^ 

 ways ; either the organisms are present in a nutrient, excite fermen- 

 but not fermentescible, medium (such as yeast in a 

 solution of milk-sugar), and in that case they do not 

 behave like organisms which can cause fermentation ; 



