MILK 87 



ducing it. As soon as the amount becomes injurious to the or- 

 ganism growth ceases and no more acid is formed. 



Sour milk obtained from clean milk is considered beneficial as a 

 food. In certain parts of Asia and eastern Europe it forms part 

 of the staple diet. Within recent years similar sour milk products 

 have been manufactured commercially on a large scale in western 

 countries. It has long been recognized that a mutual antagonism 

 exists between the acid-producing bacteria and those causing 

 putrefactive changes, and on this basis attempts to combat such 

 changes occurring in the intestines, which lead to so-called "auto- 

 intoxication," were early made by adding to the diet acid-forming 

 bacteria together with carbohydrates. At first the results were 

 only moderately successful. Then it occurred to Metchnikoff that 

 probably the organisms used had not the capacity to produce acid 

 in large enough quantities. In his search for a more powerful 

 acid producer his attention was attracted to Bacillus bulgaricus, 

 an organism isolated from milk in 1905 by Massol and Cohendy, 

 said to produce as much as twenty-five grams of lactic acid per 

 liter of milk in addition to smaller quantities of other acids. The 

 fact that it does not attack proteins and that it is not pathogenic 

 makes it particularly suitable for its therapeutic role. 



Putrid Milk. When boiled milk is allowed to stand at room 

 temperature it sometimes becomes bitter and has an alkaline 

 reaction. A spore-bearing group of bacteria and also certain ana- 

 erobes are responsible for this change ; they decompose the protein 

 into injurious substances resembling " ptomains." 



Ropy Milk. Bacteria which produce this condition are widely 

 distributed in nature. In Europe Bacillus lactis viscosus is con- 

 sidered the main agent. A micrococcus, two forms of streptococci, 

 and certain of the lactic acid bacilli are also able to bring about 

 the same condition. In certain European countries ropy milk is 

 considered a delicacy. It is not injurious provided the sliminess 

 is not the result of a mucopurulent discharge from the udder of 

 the cow. 



Colored Milk. A red color in milk may be due to blood if 

 the udder is diseased ; it may also appear if bacteria giving a red 



