BACTERIA IN MILK 703 



tion also takes place. Beijerinck/ 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 mUk. These may be due to a number of bacteria. A microorgan- 

 ism which is commonly found in connection with the shmy changes in 

 milk is the so-called Bacillus lactis viscosus. According to the researches 

 of Ward,^ 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 prodigiosus, 

 and others. 



" Bitter milk," a condition which has occasionally been observed epi- 

 demically, is also the consequence of the growth of microorganisms. 

 Conn,^ 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 ' in that it 

 possesses the ability of producing butyric acid. 



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

 fection, milk is second only to water, and deserves close hygienic at- 

 tention. A large number of infectious diseases have been traced to mUk, 

 although the actual proof of the etiological part played by it in such cases 

 has often been difficult to adduce and has necessarily been indirect. 

 Nevertheless, even when indirect proof only has been brought, it has been 

 sufficiently convincing to necessitate the most careful investigation into 

 milk supplies whenever epidemics of certain infectious maladies occur. 



Typhoid-fever epidemics have been frequently traced to milk in- 

 fection, and, in this disease, milk is, next to water, the most frequent 

 etiological factor. Schiider,' in an analysis of six hundred and fifty 

 typhoid epidemics, found four hundred and sixty-two attributed to 



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



2 Ward, Bull. 165, Cornell Univ. Agri. Exp. Stat., 1899. 

 » Conn, Cent. f. Bakt., ix, 1891. 



= Wagmann, Milchztg., 1890. 



• Schiider, Zeit. f. Hyg., xxxviii, 1901. 



