FERMENTATION. 95 



that in the one we have a single ferment only, playing its 

 part, acting on qomparatively simple and non-complicated 

 media, whilst in the other we have a complex substratum 

 for the growth of the organisms and a considerable variety 

 of organized ferment cells. 



. Fermentation may be considered from two points of view — 

 first, as merely a chemical process which is started by the 

 products of micro-organisms or yeasts, in which it resembles 

 many other chemical reactions which are initiated by light, 

 heat, a blow, or some other molecular activity unassociated 

 directly with organic life ; whilst, under the second heading, 

 it may be looked upon as due to the action of living proto- 

 plasm or cells, special fermentations being induced by special 

 organic forms. The . soluble products of these organisms, 

 however, appear to play a secondary part in the process of 

 fermentation, some accelerating, others interfering with it. 

 The process appears to be associated with the necessity which 

 there is for the organized ferments to obtain certain elements 

 for their growth and development — elements which can only 

 be obtained under special conditions, and which, if obtained 

 otherwise, do not lead to the breaking down of the substance 

 which should be fermented in the usual fashion. 



As we have already seen, the early history of bacteriology 

 was almost entirely associated with the work that was done in 

 connection with fermentation, and it was not till Cagniard- 

 Latour demonstrated that his yeast was made up of small cells 

 which appeared to be capable of reproducing themselves by 

 budding, that the inevitable conclusion was drawn that these 

 globules of yeast were really composed of vegetable proto- 

 plasm, and that it was in consequence of their growth and 

 proliferation that sugar solutions underwent the process of 

 fermentation with the evolution of carbonic acid gas and 

 the production of alcohol. Schwann and Kiitzing, indepen- 

 dently, arrived at the came conclusions after obtaining the 

 same results, and other observers' soon corroborated the 

 observations made by these pioneers, although the whole 

 facts were not discovered at once, and the knowledge of the 

 structure and life-history of the yeast-cell that we now 



' Kieser, 1814 (Schweigger's Journal, No. 12, p. 229) described spheri- 

 cal corpuscles, all of nearly the same size, which were transparent and 

 motionless, and Desmazieres depicted yeast globules in 1826 ("Aim. des 

 Sciences Naturelles," p. 4). 



