WHAT IS THE PURE YEAST OF PASTEUR? 153 



vated a few times in wort and then it is examined under the 

 microscope, and by means of my method of analysis by spore 

 formation. When wild yeast is present in such small traces 

 that could not be detected by previously known methods, 

 the treatment with tartaric acid will cause them to develop 

 sufficiently strongly to render their detection easy. The 

 same also holds good for some of the species described 

 under the name Mycoderma cerevisice. For this analysis, 

 therefore, I recommend the occasional employment of the 

 described method of treatment with tartaric acid. 



4. As formerly, I should still prefer to avoid all criticism 

 of Pasteur's work, but my opponents have not permitted this. 

 When we examine more closely as to what Pasteur really 

 meant when he spoke of the preparation of a pure yeast for 

 brewery purposes, we do not find any such definite statement 

 in his work as we could wish, but there is much to indicate 

 that he himself recognised the limit of his methods (' Etudes 

 sur la biere,' p. 227), and that his object was merely to free 

 the yeast from bacteria. Where he gives an account (loc. cit., 

 pp. 4-7) of the disease micro-organisms, which, in his opinion, 

 are able to attack beer, it is, therefore, only bacteria which 

 he describes, and there is no mention of alcoholic ferments. 

 (This view is, as was previously stated, also held by Velten, 

 and has likewise been expressed by Duclaux in both of his 

 works, namely, * Chimie biologique,' 1883, p. 618, and ' Le 

 microbe et la maladie,' 1886, pp. 91-95). After mentioning 

 the different methods which he employed in 1876 for the 

 purification of yeast, Pasteur says (p. 227) : " The best way 

 to determine whether a yeast is pure or not, is to use some 

 of it for making some beer in a two-necked flask ; when the 

 fermentation is at an end, the flask is placed in an incubator 

 at 20-25 C. .If, after some weeks, the beer does not become 

 cloudy nor covered with a film, if the sedimentary yeast 

 appears to be pure when examined under the microscope, 



