TORULA. 399 



Torula Yeasts fermenting Lactose. 



Duclaux found a yeast-fungus in milk which induces 

 alcoholic fermentation in a solution of lactose. This fungus 

 appears to be most closely related to the Torula species. 

 The cells are 1-5 to 2-5 //. in diameter, and almost spherical. 

 According to Duclaux's experiments, this yeast is more 

 aerobic than the ordinary alcoholic yeasts. Even with strong 

 aeration of the liquid, the whole of the lactose is used up 

 in the alcoholic fermentation. In a 5 per cent, solution of 

 lactose 2-5 per cent, of alcohol was formed in eleven days 

 at 25 C. The most favourable temperature for the fermenta- 

 tion of a neutral solution is 25 to 32 C., whilst at 37 to 

 40 C. the fermentation ceases. Small quantities of acid have 

 a retarding influence on the fermentative activity of this yeast. 



Adametz likewise describes a budding-fungus which fer- 

 ments lactose (" Saccharomyces lactis "). Since this fungus 

 does not yield endogenous spores, it must be classed in the 

 group of non-Saccharomycetes. The cells are of about the 

 same size as those of brewery yeasts, and are spherical and 

 elliptical. The colonies grown on peptone-gelatine are round, 

 with slightly jagged borders, and are of a dark brown 

 colour. A stab-culture in wort-gelatine yields a dull, flat 

 mass on the surface and a vigorous growth in the puncture 

 channel, and from this numerous offshoots penetrate into the 

 gelatine. In sterilised milk this fungus induces fermentation 

 phenomena within twenty-four hours at 50 C., in forty-eight 

 hours at 38 C., and in about four days at 25 C. In this 

 fermentation the lactose alone is decomposed. 



Both of the species mentioned above have been more closely 

 investigated by Kayser, together with a new species, which 

 likewise ferments lactose, and belongs to the non-Saccharomy- 

 cetes. All three yield colonies on gelatine, which are more 

 widely spread than those of beer- and wine-yeasts ; in the 

 middle of the colonies there is a thick portion, while the border 

 resembles mycelium. In milk and in neutral liquids, when 

 sufficiently aerated, they induce an appreciable fermentation 

 at 25 to 30 C. The milk does not coagulate or become 

 viscous during the alcoholic fermentation. All three species 



