22 STUDIES ON FERMENTATION. 



which is only devised after the evil has evoked the complaints 

 of customers. In such a case the brewer avails himself of the 

 kindness of some other brewer to obtain a change of yeast — a 

 custom which is recognized and valued in the trade, since all 

 managers of breweries have an interest in keeping it up. The 

 brewer whose produce is most satisfactory recognizes the fact 

 that unforeseen circumstances may compel him at any moment 

 to change his yeast. 



We have frequently had occasion to sliow that this necessity 

 for a change of yeast depends, in most cases, on some change 

 brought about by the presence of diseased ferments, the multi- 

 plication of which has resulted fortuitously from some uncon- 

 scious neglect during the process of brewing, or from climatic 

 influences. When we reflect that yeast is a living being, and 

 that the medium which serves as its aliment, and the water in 

 which it lives, are remarkably well adapted for the development 

 of a vast number of other microscopic beings, the comparative 

 purity of yeast should surprise us even more than its deteriora- 

 tion does. 



Now by means of microscopical observations we might often 

 detect the existence of the evil long before we are warned 

 of it by a defective working, wliich invariably entails great 

 losses.* 



In proof of this remark we may cite the following facts. In 

 the month of September, 1871, we were permitted to go through 

 a large London brewery, in which the microscopical study of 

 yeast was altogether unknown. We were allowed to make 

 certain experiments in the presence of the managers of the 

 establishment. We first examined porter yeast, which was 

 collected in a channel that received the yeast as it worked out 

 of the fermenting vessels. One of the ferments of disease 

 abounded in this yeast, as may be seen in the accompanying 



* Since the publication of the author's " Studies on the Diseases of 

 Wine, and the Dangers resulting to Wine and Beer from the Microscopic 

 Parasites found therein," some intelligent brewers havejderived consider- 

 able profit from the application of the theories laid down in that work. 



