BACILLUS ACIDI LACTICI. 863 



deposit is formed, and in the neighbourhood the sub- 

 stance of the potato assumes a deep greyish-blue colour. 

 At times the gelatine has a more greenish shade ; distinct 

 green colour is produced, for example, in solutions of tar- 

 trate of ammonia, of leucine, asparagine, &c., but this 

 green pigment only represents a lower stage of oxidation 

 of the blue, and can be transformed into the blue by oxi- 

 dising agents. When inoculated in sterilised milk the 

 bacilli cause no coagulation and no acidity, but gradually 

 produce a slightly alkaline reaction ; further, a slate-grey 

 colour, which, however, on the addition of acid becomes 

 an intense blue, appears in the first instance in the layer 

 of cream, and then spreads clown wards through the 

 whole fluid. In milk which has not been sterilised, and Character of 

 in which the lactic acid bacilli are growing at the same 

 time, the colour is sky-blue from the first. In milk the 

 colouring matter seems to be formed at the expense of 

 the casein, while the milk sugar remains unaltered ; the 

 bacilli, however, are able to build up the colouring matter 

 synthetically in fluids which only contain lactate of 

 ammonia, or tartrate of ammonia without any albumen. 

 The optimum of temperature for the production of the 

 pigment is from 15 to 18 C. ; above 25 C. the pigment 

 production is delayed ; at 37 C. no colouration of the 

 nutrient solution occurs. The pigment is not an aniline 

 dye, but more accurate investigations as to its properties 

 and its nature are still wanting. The bacilli and the 

 milk in which they are growing have proved to be quite 

 harmless to animals, even when injected into the veins. 



Among the bacilli which cause fermentation of carbo- 

 hydrates, the following must be mentioned : 



Bacillus acidi lactici. 

 (Lactic acid bacteria.) 



The phenomenon which has been for a long time well 

 known, that when milk is kept for some time the milk 

 sugar becomes transformed into lactic acid, and, as a 



