132 MICRO-ORGANISMS AND FERMENTATION. 



see clearly into the relations of the different alcoholic ferments 

 occurring in fermenting liquids. PASTEUR was therefore unable 

 to get beyond the indefinite conjectures and contradictory 

 views of his predecessors. In his review of the micro-organisms 

 which cause diseases in beer, he speaks only of bacteria ; and 

 the view that these are the only causes of diseases in beer has 

 since been repeatedly expressed by DUCLAUX in 1883, and by 

 other French, English, and German writers. PASTEUR, basing 

 his views on these studies, recommended brewers to purify their 

 yeast ; and in order to free it from bacteria, advised its cultiva- 

 tion in a sugar solution containing tartaric acid, or in wort 

 containing a little phenol (see below). 



In contradistinction to this, HANSEN, in the year 1883, 

 enunciated his doctrine that some of the most dangerous and 

 most common diseases of low-fermentation beer were caused, not by 

 bacteria, but by certain species of Saccharomyces, and that each of 

 the names employed by REESS, namely, Saccharomyces cerevisice, 

 Sacch. Pastorianus, Sacch. ellipsoideus, represented not one but 

 several different kinds or races. He showed that varieties 

 which until then had been incorrectly grouped under the one 

 name Saccharomyces cerevisice gave products in the brewery 

 having different characters. Starting from this, HANSEN 

 elaborated his method, by means of which a pitching-yeast, 

 consisting of only one species, is employed. After some resist- 

 ance this system has been recognised and introduced into 

 practice in all countries where the brewing industry is carried 

 on. VELTEN of Marseilles, who formerly worked with PASTEUR, 

 has, however, attacked this system (1887-89), the mistake of 

 which he deems to be that HANSEN'S yeast consists only of one 

 species. He considers it an advantage in PASTEUR'S purified 

 yeast that the latter consists of several different kinds, and 

 regards this combination of various species as necessary in 

 order that the beer may acquire the desired taste and bouquet. 

 HANSEN'S latest investigations show how completely this 

 doctrine breaks down. HANSEN proved by experiment that 

 when yeast is treated with tartaric acid, according to PASTEUR'S 

 method, the conditions are so favourable for the development of 

 the yeasts producing disease, that finally the culture-yeast is com- 

 pletely suppressed. PASTEUR subsequently greeted HANSEN'S 



