LOW-FERMENTATION YEASTS. 321 



The first race chiefly exhibits slightly elongated cells, 

 amongst which somewhat smaller pointed individuals dis- 

 tinguished by granular contents are not infrequently found. 

 If the yeast is taken from the fermenting vessel, washed with 

 water, and placed for a short time on ice, it will be observed 

 that the whole cell content rapidly changes to a granular 

 structure, and if maintained under these conditions for several 

 days, it will be found that the number of dead cells rapidly 

 increases. The second race behaves in quite a different way. 

 The cells are short and oval, or almost spherical, under normal 

 conditions in the fermenting vessel ; only a few bent indi- 

 viduals are observed, and in a washed condition the cells 

 retain their clear or slightly granular contents for a long time ; 

 very few dead cells are observed even after long preservation 

 in this condition. 



If each of the growths is placed on moist gypsum blocks, 

 maintained at the same temperature, and their further develop- 

 ment observed from day to day, it will be seen that the two 

 races behave quite differently, assuming that the temperature 

 lies within the limits for the growth of spores. Race II. forms 

 fully ripe spores at a time when Race I. does not show a trace 

 of these organs of propagation. 



The following distinctions are of value in practice in 

 determining the two races : 



In order to obtain the normal course of the primary fer- 

 mentation it is essential that Race I. should be introduced at 

 a somewhat higher temperature (7-5 C.) than Race II. Larger 

 quantities of /. than of //. must be used for pitching, in the 

 proportion of 66 to 58. The time of setting and of frothing 

 naturally differs. Both phenomena appear to occur somewhat 

 earlier with Race II. than with Race I. 



The nature of the frothing and the coating of yeast differ 

 greatly. //. gives a strong high head and a dense coherent 

 cover ; /. a low head, and the liquid often shows bald patches. 

 Moreover, Race I. gives a very lasting fermentation, and, as 

 a consequence, a slower clarification than Race II., which 

 when pure gives a particularly bright clarification. The 

 sedimentary yeast in the vat lies more compactly, and the 

 colour of //. is somewhat lighter than that of /. 



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