70 FERMENTS AND MICRO-PARASITES. 



I. MICRO-ORGANISMS AS THE EXCITING AGENTS OF 

 FERMENTATION AND PUTREFACTION. 



Gradual Development of the Vitalistic or Germ Theory. 



Before Schwamrs discovery the essence of the ferment- 

 theorganic ative process and especially of the alcoholic or vinous 

 yeast fermentation in which sugar is broken up into alcohol 



and carbonic acid was by some not at all associated 

 with the yeast, which was looked on as only an acci- 

 dental accompaniment ; by others the role of the yeast 

 was regarded as an etiological one, but only in the sense 

 that the mass of these cells acted as a porous body 

 which easily condensed the oxygen, passed it over to the 

 other substances, and thus occasioned the decomposition 

 of the sugar (Braconnot, 1831), or that the yeast pos- 

 sessed catalytic properties, and thus had the power of 

 splitting up the fermentescible substances in the same 

 way as peroxide of hydrogen is decomposed by finely 

 divided platinum, &c. (Berzelius, 1827). Up to this 

 time no one had held the view that the process of fer- 

 mentation was closely connected with the living multi- 

 plying yeast cells, and was in fact the result of their 

 life, and no one could hold such a view previously, 

 because the organised nature of yeast w<as not yet 

 known. Schwann was the founder of the vitalistic or 

 germ theory. As the result of new experiments he 

 asserted that the cause of the fermentation was the 

 vegetation and multiplication of the living yeast in the 

 fermentescible fluid, that the yeast cells took from it 

 the materials necessary for their growth, and that the 

 elements which were not taken up by the yeast became 

 grouped together principally in the form of alcohol. 

 Schwann's experiments were repeated several times in 

 the course of the next few years, and the results were 

 confirmed and extended ; among the more immediate 

 advances it is only necessary to mention the proof 

 furnished by Liidersdorff that triturated yeast cells are 

 inoperative, and that only intact cells can produce fer- 

 mentation, and also the observation by Blondeau that 



