FERMENTATION. 



101 



not really specific characteristics. He finds that within 

 certain limits the same species, under different external 

 conditions, may exhibit very different appearances, but he 

 also holds, and brings forward very strong proof in support 

 of his position, that there are limits to the influence which 

 can be exerted on the cells of a species, and that different 

 species exhibit very different characteristics when placed 

 under similar conditions ; thus, for example, Saccharomyces 



Photomicrograph of Saccharomyces Cerevisiae. x 500. Mother cells with small 

 buds coming off. Yeast from an Edinburgh Brewery. 



cerevisiae, when developed in the ordinary manner and then 

 grown vigorously for twenty-four hours at a temperature of 

 27 C., exhibits the ordinary appearance of rounded or ovoid 

 cells with a formation of septa in some cases, and with more 

 or less well-developed cells in others ; whilst this same 

 organism, when cultivated at 7.5 C., occurs in the form of 

 dense colonies with beautiful mycelium-like branchings. 



