PRODUCED BY ALCOHOLIC FERMENTS. 173 



organisms are distinguishable by their form from yeast cells, 

 he recommended that a microscopic examination should be 

 made in the brewery, both of the pitching yeast and of the 

 beer. He described several methods for the purification of 

 yeast, but for this purpose he especially recommended culti- 

 vation in a solution of cane sugar containing a little tartaric 

 acid (p. 224). At all events it was this method in particular 

 which was recommended by his pupils. 



With regard to the yeast cells Pasteur repeated in several 

 parts of his work (especially on pp. 218-220) the views of 

 previous investigators, Reess, Engel, Holzner and Lintner. In 

 other places (e.g. p. 193), he appears, however, to have 

 adopted the opposite view of Cienkowski and Harz, namely, 

 that the cells of yeast are subject to an endless and rapid 

 variation, and that there are no fixed species of Saccharo- 

 myces (and consequently also no species of disease-yeasts). 

 In agreement with this is also the opinion which he 

 expresses on p. 333 that, under conditions obtaining in the 

 brewery, low beer-yeast can become changed into high-yeast. 

 He investigated (p. 199) a special form of yeast (caseous 

 yeast) which he found in an English brewery-yeast, and he 

 suggests as possible that this might be a form of development 

 of the culture yeast. Where he discusses the yeast fungi, 

 everything is in a state of uncertainty ; nowhere does he 

 indicate any certain boundary lines. 



With regard to the question of pleomorphism, Pasteur's 

 view was similar to that held by Bail, since he assumed that 

 the Saccharomycetes were forms of development of certain 

 brown mould fungi (Dematium and Alternaria) which are 

 found on the surface of different fruits (pp. 154-155, 

 164-165, 177). It is easy to undertand how Pasteur could 

 acquire such an erroneous conception when we recollect that 

 he never made a distinction between the Saccharomycetes 

 (yeast cells with endospore-formation) and the non- Saccharo- 

 mycetes (yeast cells giving no endospore-formation). His 



