194 MICRO-ORGANISMS AND FERMENTATION. 



alcoholic fermentation. All three species ferment lactose, 

 galactose, cane-sugar, glucose, invert-sugar, and finally 

 maltose, but the last only with great difficulty. In 

 the fermentation of milk-sugar with these yeasts, the 

 resulting liquids are as rich in alcohol as the strongest 

 beers. Kayser remarks that it may perhaps be possible 

 to make practical use of this observation and by means 

 of these fungi to convert the large quantities of whey, 

 obtained in the manufacture of cheese, into an alcoholic 

 liquor. 



Beyerinck has described two yeasts which also ferment 

 milk-sugar, and which must be provisionally regarded as 

 non- Saccharomycetes ; these are Saccharomyces KepTiir, 

 which occurs in kephir-grains and consists of longish, 

 variously-formed cells, and forms slightly jagged colonies on 

 gelatine; and Saccharomyces Tyrocola, which consists of 

 small roundish cells, and forms snow-white colonies on 

 gelatine. Beyerinck found that these two species secrete a 

 particular invertive ferment (lactase) which inverts not only 

 cane-sugar but also milk-sugar ; it does not, however, invert 

 maltose. Lactase can be prepared as follows : A five per cent, 

 solution of milk-sugar, containing also nutrient salts and 

 asparagine, is fermented with kephir-yeast ; the product is 

 filtered and the ferment is precipitated from the filtrate by 

 the addition of alcohol. According to Schuurmans Stekhoven, 

 however, the enzyme of Beyerinctis kephir-yeast does not 

 invert milk-sugar. 



It was previously proved by Bourquelot that Aspergillus 

 niger contains a soluble chemical ferment which has some 

 similarity to the invertase of beer-yeast, but is distinguished 

 from the latter by its property of converting maltose into 

 dextrose. He points out, however, that two ferments may 

 possibly be present, just as diastase is now regarded as a 

 mixture of several ferments. A doubt of this nature will 

 always arise when a soluble chemical ferment is found to 

 vary in its action. 



