236 MICRO-ORGANISMS AND FERMENTATION. 



Austrian Erxleben in 1818 was the first who definitely expressed 

 the thought that fermentation " appears in no way to be a 

 simple chemical operation, but rather is in part a process of 

 growth, and should be regarded as the link in the long chain 

 of nature which combines those actions that we describe as 

 chemical processes with those of vegetative growth." But 

 this must be regarded only as a hypothesis without further 

 foundation. 



Twenty years later, and almost simultaneously, three 

 scientists expressed clear and definite views based on direct 

 experiments regarding the dependence of alcoholic fermenta- 

 tion upon yeast cells. 



It may be of interest to see how they arrived at the 

 same result in three different ways. 



Cagniard-Latour was the first to publish his work on yeast, 

 in 1835-37. In his studies of beer and wine fermentation, 

 both in practice and on the small scale, he observed that the 

 yeast globules rise to the surface of the beer-wort on account 

 of the entangled gas w r hich they produce. They possess 

 the power, by budding or by elongating their own tissues, of 

 multiplying, and in this way producing manifold globules, 

 which separate from each other when fully grown. He thus 

 confirmed his view that yeast cells are organic, and belong to 

 the vegetable kingdom. During propagation they are nour- 

 ished by the beer-wort, and when the fermentation has come 

 to an end the liquid contains many times the quantity of yeast 

 that was added to it, whereas the earlier view was that the 

 substantial precipitate consisted mainly of secretions. He also 

 found that yeast will not propagate in pure sugar solutions. 



His researches enabled him to conclude that in all pro- 

 bability it is the yeast cells that destroy the stability of the 

 components of sugar, and bring about its decomposition into 

 alcohol and carbon dioxide ; that fermentation, in fact, is 

 .a result of vegetable activity. 



The same observation regarding the vegetable character 

 of yeast was made simultaneously, or a short time after, and 

 quite independently by Theodor Schwann. It has already 

 been mentioned that he made important contributions to the 

 discussion of the generation of living matter, and it was these 





