1 84 "DISEASES" OF BEER, 



in general, so also micro-biology has received a very power- 

 ful impetus through the epoch-making theories of Darwin 

 concerning the transformations of species. This has been 

 brought about, especially, by Nageli's work, which was men- 

 tioned above. 



Finally, stress must be laid upon the reciprocal action which 

 there has always been between micro-biology and chemistry, i 



All these different lines of investigation have mutually 

 helped and have reacted on one another in many ways. If 

 in the above description we had been able to further dwell 

 upon the subject, more life and fulness could have been given 

 to it, but this would have carried us beyond the limits of this 

 treatise. 



3. MY INVESTIGATIONS. 

 Problem and Method. 



In the foregoing historical portion of this treatise we 

 have seen how, in the course of time, guesses were thrown 

 out in all directions, and the most varied possibilities were 

 considered in order to explain the relationship which the 

 alcoholic fungi bear to the diseases of beer, and that as often 

 as the right road was on the point of being struck, it was 

 again soon abandoned on account of some unskilful turn, just 

 as if the wrong direction had been aimed at. 



After the appearance of Nageli's work, the idea of the 

 degeneration and transformation of brewery yeast was, as we 

 have seen, brought to the front. It was in such occurrences 

 that the cause was sought of those diseases in the beer, and 

 those troubles in working, which it was assumed were brought 

 about by the yeast. Thus, the other possibility was more and 

 more lost sight of namely, that the cause of these troubles 

 might also be attributed to foreign species which had gained 

 admission, and which, in their competition with the culture 

 species, had given rise to the symptoms of disease. As 



