688 BACTERIOLOGY OF MILK 
The origin and relation of streptococci to milk-borne epidemics of 
septic sore throat and tonsillitis have been subjects of controversy. 
There appear to be two theories : one theory maintains that the strep- 
tococci are of bovine origin and presumably derived from the udders 
of cows which are suffering from mastitis or garget. The other theory 
assumes that these streptococci are usually of human origin and have 
gained entrance to the milk at some stage of its postbovine history. 
Theobald Smith and Brown^ have made an extensive study of this 
subject and their conclusions are of particular interest in this con- 
nection. They state that "there is at present no satisfactory evidence 
that bovine streptococci associated with mastitis or garget are the 
agent of tonsillitis in man. Whenever cases of garget are suspected as 
sources of infection in man, both human and bo\ine types should be 
looked for." 
The most numerous of the saprophytic bacteria commonly found 
in raw milk belong to the group of organisms which form lactic acid, 
but no gas, from lactose. They are frequently referred to as lactic 
acid bacteria, but this name is not wholly apjiropriate nor is it dis- 
tinctive; many unlike organisms possess this property in common. 
The best known and most widely distrilnited of these lactic acid 
bacteria is a streptococcus. Streptococcus lacticus,'- an organism which 
is present not only in moderate numbers in the feces of the cow, but 
also upon the udder and flanks of the animal as well if cleanliness is 
not strictly observed. The initial infection of milk with Streptococcus 
lacticus is usually not extensive, but milk appears to be a particularly 
favorable medium for its development, and even after a few hours 
the organism may have increased greatly in numbers if the tempera- 
ture conditions are favorable. The most noteworthy chemical change 
associated with the growth of Streptococcus lacticus is a rapid accu- 
mulation of acid, principally lactic acid, which soon results in an acid 
coagulation of the casein. The degree of acidity is usually sufficient 
to inhibit the development of proteolytic bacteria and also a majority 
of pathogenic bacteria as well. Occasionally other types of fecal 
bacteria may be isolated from milk. Of these B. coli has received 
much attention, chiefly through its constant association with human 
as well as with bovine excrement. Papasotiriu and Prescott^ \\2i\e 
isolated bacteria indistinguishable from Bacillus coli by cultiu-al 
methods from hay and dried grains. Consequently the identification 
of it in milk does not furnish conclusive evidence of contamination 
either from human or bovine sources. B. coli does not produce more 
than minimal amounts of gas in milk, although its aerogenic activity 
in glucose and lactose broth is one of its noteworthy cultural characters. 
It does, however, form sufficient acid from lactose to cause an acid 
1 Jour. Med. Res., 1914, 31, 501. 
2 Knise: Centralbl. f. Baktcriol., orig., 1903, 34, 737. Heiiienianii: Jour. Infec. 
Dis., 1906, 3, 173. 
3 Centralbl. f. Bakteriol., ref., 1903, 33, 279. 
