ALCOHOLIC FERMENTS. 



201 



breweries, forms variously-shaped cells. The cells are usually 

 transparent and less refractive than the true Saccharomycetes ; 

 in each cell there are generally one, two, or three highly 

 refractive particles, which often have a quivering, rolling 

 motion. This micro-organism forms a dull, greyish, wrinkled 

 film on wort and beer, and does not excite alcoholic fermen- 

 tation ; neither does it invert solutions of cane-sugar. 



The colonies on the surface of the gelatine are bright, 

 grey, dull, and spread out like a film or hollowed like a shell. 

 By means of this macroscopic appearance Mycoderma is 

 readily distinguished from the ordinary Saccharomycetes 



FIG. 54. 



Mycoderma cerevisise from Copenhagen breweries. Drawn from nature 



by Holm. 



which, on the same medium, form bright greyish-yellow 

 colonies with a dry or lustrous surface, and of a more or less 

 arched form. Sacch. membrancefaciens (page 177), which 

 differs so markedly in its biological behaviour, and which very 

 rapidly gives a strong film on the liquid, alone resembles 

 Mycoderma also in its behaviour on plate cultures. 



The form of film described above was obtained by Hansen 

 when lager beer was exposed in open vessels at temperatures 

 between 2 and 15 C. ; at 33 C. a development still 

 occurred, but at temperatures above 15 C. this species gave 

 place more and more to competing forms. Therefore, since 

 low temperatures are favourable to its development, it will 



