328 MICROBIOLOGY OF MILK AND MILK PRODUCTS. 



of organisms is an important factor here. In making comparisons of 

 this sort, it is, of course, necessary that the different samples be held at 

 the same temperatures. 



MILK AS A CARRIER or DISEASE-PRODUCING ORGANISMS. 



It is not the purpose of this chapter to discuss in detail the diseases 

 which may be carried by milk, but a chapter on bacteriology of milk 

 would be incomplete without a brief discussion of this important subject. 



From the standpoint of their relation to the health of the consumer 

 the microorganisms in milk may be divided into three groups. 



THOSE MICROORGANISMS WHICH ARE BENEFICIAL AND DETRIMENTAL 

 TO HEALTH. Acid Forms. The preservative properties of sour milk 

 have been known since very ancient times. Its use as a preservative 

 for meat, eggs and other perishable food products demonstrates the value 

 of sour milk as a means of preventing decomposition. It has also been 

 known for a long time that sour milk has a certain therapeutic value 

 because of the action of the lactic bacteria in preventing harmful 

 fermentations in the digestive tract. More recently the work of Metch- 

 nikoff has shown the usefulness of sour milk both for the treatment and 

 prevention of intestinal disorders by preventing the development of the 

 putrefactive bacteria in the digestive tract. In view of the value of sour 

 milk for preventing certain forms of disease and its inhibiting action on 

 certain undesirable organisms the Bact. lactis acidi type of bacteria must be 

 regarded as beneficial organisms, and from the standpoint of the health of 

 the consumer their presence in the milk is to be welcomed rather than 

 discouraged. As the value of sour milk drinks becomes better known 

 the importance of this group of milk bacteria will be more fully recognized 



Neutral Forms. In ordinary milk there is a large class of bacteria 

 which, so far as known, have no appreciable effect either upon the com- 

 position of the milk or the health of the persons consuming it. This group 

 includes a number of species, many of them being coccus forms, 

 some of them appearing in plate cultures as chromogenic colonies. 

 They grow more or less freely in milk, depending upon the conditions, 

 but they are usually held in check by the acid-forming bacteria and do 

 not constitute a very important part of the flora of normal milk. They 

 are, therefore, of little significance from the practical standpoint except 

 as they indicate the conditions under which the milk has been produced 

 and handled (p. 312). 



