METHODS OF STUDYING THE YEASTS 159 



of contamination. The use of the ruled cover glass on which each 

 square is numbered, makes it possible to follow closely each stage 

 in the development of the yeast. One is thus able to follow the modi- 

 fications which occur at regular intervals. By this method the 

 phenomena of budding, sexuality, sporulation, germination of spores, 

 etc., may be watched. When this apparatus is used for the study of 

 germination of spores, certain difficulties are encountered. In a 

 yeast which sporulates there are always a few cells which have not 

 formed ascospores. When transferred to a new medium, the as- 

 porogenous cells develop more rapidly. Thus, for example, a dilu- 

 tion of beer yeast placed in a Bottcher moist chamber may include 

 asporogenous cells mixed with ascospores. Their early development 

 hinders observation. The simplest method to get around this is to 

 kill the vegetative cells with heat; 1 the spores being more resistant 

 will pass through such treatment. 



In order to carry outr this, one should proceed as follows : A portion 

 of yeast growth from solid media (agar, gelatin, carrot, etc.) is spread, 

 by means of a spatula, on a sterile cover slip. This is then placed 

 in an incubator at 55-60 for 12 hours. The vegetative cells are not 

 able to withstand this temperature and only the ascospores survive. 

 The yeast is then moistened with a drop of water and a drop is placed 

 in a Bottcher moist chamber. The vegetative cells will remain in the 

 solution but should cause no difficulty since that will not germinate. 

 Guilliermond found this method a convenient one for studying the 

 germination of ascospores. 



Lindner 2 extolled very much a method which he devised and termed 

 the adhesive culture. This method simply consists in applying a thin 

 layer of the yeasts or other organisms to a cover slip which is even- 

 tually placed in a humid chamber. Let us suppose that we wish to 

 study the bacteria in our saliva. All that would be done would be to 

 apply the tongue to a sterile cover slip. The organisms remain ad- 

 herent to the cover slip and develop in their own natural medium. 

 The colonies may be sufficiently well isolated for picking pure cultures 

 by means of a platinum wire. In this way, this procedure may be 



1 Another method by which the same results may be obtained has been de- 

 vised by Hansen. This investigator has stated that the vegetative cells, perhaps 

 on account of their age, are killed by a period of one minute in absolute or 50 per 

 cent alcohol. The ascospores, in a state of maturity, resist the alcohol for a long 

 time. This constitutes a simple method of getting rid of the vegetative cells 

 when only ascospores are desired. (Hansen, Ueber die totende Wirkung des 

 Aethylalkohols auf Bakterien und Hefen. Cent. Bakt. 45, 1907.) 



2 Lindner, P. Die Adhasionkultur, eine einfache Methode zur biologischen 

 Analyse von Vegetationsgemischen in natiirlichen oder kiinstlichen Nahrsubstraten. 

 Zeitschr. Spir. Industrie, No. 46 and 47, 1901. 



