LACTIC FERMENTATION. Although lactose or sugar-of-milk may, under certain conditions, be made to undergo alcoholic fermentation (as in the preparationaaf ktuniss by the Tartars from mares' milk), it generally yields a very different product, viz., lactic acid, as may be seen in the case of milk turning sour in warm weather. The cascine is usually considered to act as the ferment, but being insoluble in acids. it is thrown down in flakes as soon as the milk becomes sour. In this insoluble form, it exerts little action , in converting the lactose into lactic acid but if the acid be' neutralized by carbonate of soda or by chalk, the curd is redissolved, and the transfor mation of the sugar into lactic acid is renewed. No evolution of gas or absorption of oxygen takes•place during the conversion of the sugar into the acid.
Not only sugar-of-milk, but cane sugar, starch, dextrine, and gum pass readily into lactic acid under the influence of caseine or other animal matters undergoing decompo sition.
Pasteur considers that a specific ferment, the germs of which exist in the atmosphere, ;s concerned in the production of the lactic fermentation. During the process recom .nendel in the preceding article for the preparation of lactic acid, a layer of particles of a gray color is observed on the surface of the sediment. This substance, when exam ined under the microscope, is seen to consist of little globules or very short articulations, constituting irregular flocculent particles much smaller than those of beer-yeast, and exhibiting a rapid gyratory motion. When washed with a large quantity of water, and then diffused through it solution of sugar, the formation of lactic acid at once com mences. Hence it follows that these organic particles, and not the caseine, arc the actual agents in the conversion that takes place.