VII. 



BACTERIA IN ARTICLES OF FOOD. 



Milk always contains bacteria, unless drawn with special precau- 

 tions into a sterilized flask. In the healthy udder of the cow it is 

 sterile, but in tuberculous cows, when the milk glands are involved, 

 tubercle bacilli may find their way into the milk in considerable 

 numbers. Ag ordinarily obtained and preserved, milk is greatly ex- 

 posed to bacterial contamination from various sources ; desquamated 

 cuticle from the external surface of the udder and from the hands of 

 the milker, and floating particles from the air of the stable, fall into it 

 at the very moment it is drawn, and it is subsequently contaminated 

 by bacteria from the air, and from water used in washing the recep- 

 tacles in which it is placed or added to it by the thrifty milkman. 

 As it furnishes an excellent nutrient medium for many of the bacteria 

 which are thus introduced into it, under favorable conditions of tem- 

 perature it' quickly undergoes changes due to the multiplication in it 

 of one or more of these microorganisms. The acid fermentation and 

 coagulation of the casein which so constantly occurs is completely 

 prevented by sterilizing fresh milk in flasks provided with a close- 

 fitting cork or cotton air filter. Numerous researches have been 

 made with reference to the microorganisms found in milk and the 

 various fermentations to which they give rise. Naturally a great 

 variety of species will be found in an extended research, but all are 

 accidentally present, and only those demand special attention which 

 produce the various fermentations of this fluid commonly encoun- 

 tered, or which have special pathogenic properties. 



Several different bacteria produce an acid fermentation and con- 

 sequent coagulation of milk, but the usual agent in producing this 

 fermentation is the Bacillus acidi lactici, which is identical with the 

 " ferment lactique " of Pasteur. When a pure culture of this bacillus 

 is introduced into sterilized milk kept at a temperature of 25 to 30 C. , 

 coagulation occurs in from fifteen to twenty-four hours. A uniform, 

 gelatinous mass is produced which does not subsequently become 

 dissolved (Adametz). Various other bacteria produce a similar 

 change, including a number of common water bacteria, several spe- 



