MORPHOLOGY AND ANATOMY OF YEAST CELLS. 



295 



perature minimum for film-formation is lower than that of 

 spore-formation. 



In brewers' low-fermentation yeasts, and in some wild 

 yeasts, Will observed round and oval cells, having a thick 

 membrane and containing a number of small oil-drops (Fig. 48). 

 These occurred in the rings of yeast and in the small surface 

 patches preceding true film-formation. If treated with con- 

 centrated hydrochloric acid, the membrane splits into two 



a. 



Fig. 48. Resting cells (after Will). The outer layer is partly or completely detached, 

 a, b, in wort ; c-f, in mineral nutrient solution. 



layers. In cultures, especially in artificial nutrient liquids, 

 the outer layer of this membrane gradually detaches itself ; 

 sometimes in such a way that the outer layer is not torn, so 

 that it appears as though the one cell were contained within 

 the other. The cell contents are coloured green or brown by 

 concentrated sulphuric acid. The glycogen reaction '"with 

 iodine has been occasionally observed in the cells. They 

 appear to play a certain part in the life economy of the growth, 



