ALCOHOLIC FERMENTS. 121 



reaction taking place in the interior of the organism. They 

 regard fermentation as an alternate hydration and dehy- 

 dration. 



In all these different theories of fermentation, the main 

 point of all questions relating to the subject is not touched 

 upon : How comes it that, in these microscopic cells, the 

 plasma, which has the same appearance in the different 

 species, yet in one cell induces an acetic acid fermentation, 

 in another butyric acid fermentation ; in a third it induces a 

 direct fermentation of cane-sugar, whilst in a fourth the 

 cane-sugar becomes first hydrolysed and then fermented ? 

 The cause of these different kinds of activity of plasma 

 is still an unsolved problem. 



The theories of fermentation hitherto put forward fail to 

 give any comprehensive explanation of known facts, and con- 

 sequently they have here only an historical interest. 



From the above resume it will be seen that, at the time 

 when Hansen commenced his investigations, our knowledge 

 of the alcoholic ferments was very deficient and untrustworthy. 

 Consequently the problem had to be attacked experimentally 

 from the very foundations. Hansen has done this in the 

 work which he has now carried on for many years. 



The previous investigators had certainly gone as far as 

 was possible along the paths which they had marked out. 

 When we compare their investigations especially those of 

 Pasteur and Reess with those of Hansen, we find that the 

 latter attacked the problem from new points of view and 

 with new methods. He extended his investigations on this 

 subject far and wide in all directions. His researches have 

 not only opened up new paths from the scientific standpoint, 

 but they have also brought about a reform in the fermentation 

 industry. For these reasons it is but right that they should 

 form the ground-work of the following section of my book. 



