Udder parenchyma from freshly slaughtered, actively lactating cows was used. In 2-4 days 100 gm. of fresh gland material would use up 5 gm. of sugar. The rate was about the same for glucose, galactose, equivalent mixtures of glucose and galactose, and lactose. Lactic acid was the chief, but not the only, product of fermentation. The power of milk to reduce lactose was tested by placing milk from individual cows in collodion bags and dialyzing it against distilled water. The dialyzate was tested for reducing sugars by means of Barfoed''s reagent. Reducing power of the milk was low (0.0-0.09%). Milk glands to which had been added either toluol or thymol reduced all the disaccharides and also fermented mono-saccharides. Lactose was the most easily fermented sugar.