THE KINDS OF MICHO-ORGANISMS IN MILK 385 



growth. In other cases slime is formed by the associate action of 

 two types either one of which alone would not produce slime. 



Other Abnormal Conditions in Milk 



Bitter Milk.— A bitter taste develops sometimes in milk, and 

 is caused in most cases by action of micro-organisms. It was 

 formerly thought that some kinds of fodder, such as turnips, raw 

 potatoes, vetches, moldy hay and straw, were direct causes of 

 bitter substances passing through the mammary glands into the 

 milk. The idea was supported by the fact that a bitter taste is 

 liable to occur when cows are pasturing, since some plants con- 

 tain bitter principles. It is now believed that foods act merely 

 as carriers of micro-organisms which thus gain access to the milk. 

 This is probably the true explanation, since fresh milk rarely has 

 a bitter taste, although it may develop after the milk has been 

 standing for several hours. The taste may be noticeable after 

 five to six hours and becomes intense after twelve to twenty-four 

 hours. 



Perhaps the common cause of a bitter taste in milk is the pres- 

 ence of peptones and albumoses which are formed from the pro- 

 teins in milk by bacterial action. Liquefying cocci are the most 

 common agents, and in boiled milk the spores of members of the 

 hay bacillus group pass into the vegetative forms and multiply. 

 These digest the casein and produce a bitter taste. Undoubtedly, 

 varieties of the proteus group which are commonly present in milk 

 may digest the casein, with the production of a bitter taste. Some 

 of these peptonizing bacteria grow at relatively low temperature 

 at which lactic acid bacteria grow but slowly, and the latter, 

 therefore, do not inhibit the growth of digesting organisms. 



The presence of peptones in milk as a result of bacterial action 

 has been held to be the cause of digestive troubles, especially in 

 the intestinal tract of infants. Fliigge in particular has advo- 

 cated this hypothesis, and went so far as to claim that some of 

 these spore-bearing bacteria produce violent poisons. This argu- 

 ment has been used frequently as an objection to heating milk 

 for infant feeding. The evidence, however, is not entirely con- 

 clusive, and it is quite possible that peptones were, in reality, the 

 substances causing the trouble. Fliigge argued that heating milk 

 destroyed the vegetative forms of bacteria, including, of course, 

 the lactic acid bacteria, and that the surviving spores then would 

 grow and produce poisons, Fliigge's theory .found much favor 

 among pediatricians for some time, but as it has not been con- 

 firmed, so it has lost ground. 



Aside from bacteria that form protein decomposition products 



25 



