CHAPTER V 



VARIATIONS IN FERMENTING POWER 



The Fermentation op Cakbohtdrates. 



The process of fermentation in thecaseof themono-saccharides 

 or glucoses — the compounds most readily fermented by the 

 action of bacteria — consists of two stages, (i) the splitting of 

 the "glucoses" with the formation of acids (formic acid, 

 lactic acid) and (ii) the conversion of the acid, by a process 

 of hydration, into simpler substances most of them gaseous 

 (carbon dioxide, hydrogen, methane, etc.). In the case of the 

 di-saccharides (lactose, maltose, saccharose) an earlier stage 

 must first be completed, namely the "inversion" of these 

 substances into glucose. This preliminary change is not 

 easily recognised, but the two final stages of the process are 

 sufl&ciently indicated by the formation, respectively, of acid 

 and of gas. 



The power possessed by certain bacteria to bring about 

 the fermentation of carbohydrate compounds is subject to 

 variation to a remarkable degree. Different strains of the 

 same organism may differ from each other in their " sugar " 

 reactions. The sa/me strain may vary from time to time 

 during cultivation, apparently spontaneously. In other cases 

 the efiect can be traced to the conditions of growth and is 

 found to depend upon such factors as the temperature, the 

 presence of oxygen, the atmospheric pressure, the age of the 

 culture, the age of the medium and its composition. The power 

 to produce fermentation may be modified by symMosis. It 

 is sometimes altered in the case of carriers, after animal 

 "passage" and in the course of a disease. New fermenting 

 properties may be developed asaresultof prolongedcultivation 

 in a particular" sugar," or bya process of " artifidalselection." 



