238 MICRO-ORGANISMS AND FERMENTATION. 



nutrition and its growth, whereby those elements which are 

 not taken up by the vegetable body, are principally com- 

 bined to form alcohol (probably along with many other 

 substances)/' 



F. T. Kiitzing was the third who dealt with this important 

 problem at the same time (1834-37). Within the scope of his 

 elaborate investigations concerning the lowest microscopical 

 plants he included the yeasts and other micro-organisms that 

 usually occur in brewery wort and distillery mash, and pub- 

 lished good drawings of these growths. It is of particular 

 interest that Kiitzing was the first to investigate the mother 

 of vinegar, the slimy skin which forms on the surface of a 

 liquid that is undergoing acetic fermentation. He examined 

 this film from its earliest stage, and found that it consisted 

 of very small plants, which gradually increase in length. He 

 realised the extraordinary importance which the study, of the 

 lowest forms of life would have for organic chemistry, and 

 for the whole field of natural science. Chemistry must rule 

 out yeast from amongst its chemical compounds, as it proves 

 to be an organism, and he regarded it as certain that " the 

 whole process of the spirituous fermentation is dependent on 

 the formation of yeast, and that of acid fermentation on the 

 formation of mother of vinegar " ; " fermentation is synony- 

 mous with the vital process/' Thus he supplied a clear and 

 definite form for the vitalistic theory of fermentation in 

 opposition to Gay-Lussac's oxygen hypothesis, and to Liebig's 

 theory of the breaking down of yeast cells as the cause of 

 fermentation. 



Mitscherlich's work is also of a fundamental character. 

 In 1841 he described the yeast as consisting of round and oval 

 globules, and he solved the question of their importance for 

 fermentation through the following beautiful experiment : 

 A little yeast is placed in a glass tube, closed at the lower end 

 with a sheet of paper, and this is placed in a sugar solution. 

 In the course of several days it will be seen that fermentation 

 has actually taken place in the tube, owing to the sugar solu- 

 tion having diffused through the paper. Alcohol gradually 

 diffuses out throughout the liquid, which becomes saturated 

 with carbon dioxide, but the greater quantity of carbon 





