PURIFICATION AND ISOLATION OF YEASTS 153 



tion and speculation of yeasts. It has the disadvantage of taking 

 quite a little time with some yeasts. 



Certain varieties sporulate quickly in special media. Thus, Klocker 

 has shown that Schwanniomyces ocddentalis produces an abundant 

 spore formation on a decoction of hay with gelatin. On the other 

 hand, Saccharomyces Ludwigii sporulates in a short time in a 5 per 

 cent solution of saccharose which is a poor nutrient for this yeast. 



Other yeasts form ascospores in many common liquids when foods 

 become scarce. In this category belong the varieties of the genera 

 Willia and Pichia, which sporulate ordinarily in the pellicle on the 

 surface of the media. The Sch. octosporus is able, oftentimes, to form 

 ascospores at the beginning of fermentation. 



These are the principal methods which are employed for this pur- 

 pose. The method wherein the plaster block is used is satisfactory 

 for most yeasts and is very convenient. Certain yeasts, however, 

 furnish few or no spores with this method. The Schizosaccharomyces 

 sporulate very easily on solid media (gelatin and carrot); the Zyg. 

 japonicus shows spores only on nutrient gelatin, on Gorodkowa's 

 medium and the pellicles of cultures. Zyg. Priorianus sporulates on 

 a plaster block soaked with beer wort, on carrot and on Gorodkowa's 

 medium. Finally certain parasites demand very special conditions. 

 S. guttulatus, for example, sporulates only in the intestines of ani- 

 mals in which it lives as a parasite. This, however, is an exceptional 

 case. Zyg. major sporulates only on plaster blocks which have been 

 moistened with beer wort and on gelatin to which milk has been 

 added. 



In summarizing this question, it is well to note that the method 

 of Engel-Hansen is the most widely used and after that the proce- 

 dure of Gorodkowa. These yield most consistent results to which 

 every one has recourse for careful studies on spomlation. 



B. Methods for Purification and Isolation of Yeasts 



The purification and isolation of yeasts require delicate tech- 

 nique. In nature, it happens that yeasts are not only mixed with bac- 

 teria and other fungi but also with other yeasts. It is quite simple 

 to separate the bacteria and molds but more difficult to separate the 

 yeasts from one another. The yeasts may possess the same shape, 

 which makes it difficult to distinguish between them. Thanks to the 

 careful investigations of Hansen and Lindner, we possess today such 

 methods that the isolation may be made with fair certainty. Two 

 methods are available, the physiological and the dilution method. The 

 latter may be regarded as fractional culturing. 



