176 CHARACTERIZATION AND IDENTIFICATION 



facture. One class is able to live at higher -temperatures while the 

 other demands a lower temperature. This characteristic does not 

 seem to be constant, for a top yeast may transform itself into a bottom 

 yeast. 



Finally, certain other characteristics, as the amount of alcohol 

 produced in a fermentation, parasite or saprophyte, or pathogen, 

 may be used. Lindner has also shown that one may use the nitroge- 

 nous and hydrocarbon metabolism properties of the yeast. 



^Methods for the Characterization of the Torula, Mycoderma 

 and Pathogenic Properties 



By summing up all of the characters, one may arrive at a deter- 

 mination of a true yeast. But when a yeast is encountered which 

 does not form spores or a scum, as many of the industrial yeasts 

 and pathogens, or if it grows on the surface but forms no ascospores 

 as with the Mycoderma, the determination becomes more complex, 

 if not impossible. The most important characteristics are the tempera- 

 ture of scum and ascospore formation. The biochemical character- 

 istics and the giant colony formation remain. 



It is almost impossible to recognize most of the pathogenic yeasts 

 described in the last few years. Many of these varieties need more 

 study according to the newer methods. Leberle and Will 1 have shown 

 that many of the characteristics for the differentiation of the Myco- 

 derma and Torula should be taken from the biochemical properties 

 of the species: assimilation of various sugars, alcohol, organic acids, 

 resistance of the various varieties towards alcohol and oxidations of 

 these compounds. Lutz and Guegen, 2 from their work, have proposed 

 another method for the determination of the species which consists 

 in microscopic and macroscopic examination of the yeast on a great 

 many different media. They propose to use the following media: 



I. General Media. 



A. Raulin's solution, acid and neutral. 



B. Gelatin prepared from Raulin's solution. 

 II. Nitrogenous media with organic nitrogen. 



Raulin's solution with urea in place of the ammonium nitrate. 

 III. Media made up of different carbohydrate materials and poly- 

 atomic alcohols. 



1 Will, H. Beitrage zur Kenntniss der Sprosspilze ohne Sporenbildung. 

 Cent. Bakt. 19, 1907; 221, 1908; Beitrage zur Kenntniss der Gattung Mycoderma 

 nach Untersuchungen von Hans Leberle. Zeit. Brauw. 28, 1910. 



2 Lutz, L. and Guegen, F. De runification des methodes de cultures des 

 Mucidinees et des levures. Bull, de la Soc. de Mycologie de France, 1901. 



