BACTERIA IN MILK 1031 



Alcoholic fermentation may take place in milk as a result of 

 the activities of certain yeasts. Upon the occurrence of such fer- 

 mentations depends the production of kefyr, koumys, and other 

 beverages which have been in common use for many years, especially 

 in the region of the Caucasus. The characteristic quality of these 

 beverages is contributed by the feeble alcoholic fermentation pro- 

 duced by members of the saccharomyces group, but side by side 

 with this process lactic-acid formation also takes place. Beijerinck, 10 

 who has carefully studied the so-called kefyr seeds, used for the 

 production of kefyr in the East, has isolated from them a form of 

 yeast similar in many respects to the ordinary beer yeast, and a 

 large bacillus to which he attributes the lactic-acid formation. 



Occasional but uncommon changes which occur in milk lead to 

 the formation of the so-called " slimy milk," yellow and green milk, 

 and bitter milk. These may be due to a number of bacteria. A 

 microorganism which is commonly found in connection with the 

 slimy changes in milk is the so-called Bacillus lactis viscosus. Ac- 

 cording to the researches of Ward, 11 this microorganism is frequently 

 derived from water and it is the water supply which should attract 

 attention whenever such trouble occurs in dairies. 



The so-called blue, green, and yellow changes are usually due to 

 chromogenic bacteria, such as Bacillus cyanogenes, Bacillus prodigio- 

 sus, and others. 



' * Bitter milk, ' ' a condition which has occasionally been observed 

 epidemically, is also the consequence of the growth of microorgan- 

 isms. Conn, 12 in 1891, isolated from a specimen of bitter cream a 

 diplococcus which occasionally forms chains and which in sterilized 

 milk develops rapidly, producing an extremely bitter taste. The 

 organism of Conn differs from a similar diplococcus described by 

 Wagmann 13 in that it possesses the ability of producing butyric acid. 



Milk in Relation to Infectious Disease. As a source of direct 

 infection, milk is second only to water, and deserves close hygienic 

 attention. A large number of infectious diseases have been traced 

 to milk, although the actual proof of the etiological part played 

 by it in such cases has often been difficult to adduce and has neces- 

 sarily been indirect. Nevertheless, even when indirect proof only 



10 Beijerinck, Cent, f. Bakt,, vi, 1889. 



"Ward, Bull. 15, Cornell Univ. Agri, Exp. Stat., 1899, 



12 Conn, Cent. f. Bakt,, ix, 1891. 



" Wagmann, Milchztg., 1890. 



