MILK IN ITS RELATION TO THE PUBLIC HEALTH (iSO 
coagulation of the casein. In this respect it does not differ markedly 
from other lactic acid bacteria. Occasionally, in association with a 
strongly proteolytic bacterium, as certain strains of B. mesentericus, a 
deep-seated change is brought about in milk by the combined action of 
the two organisms. B. mesentericus acting alone liquefies the casein; 
in symbiosis with B. coli not only are the protein constituents of the 
milk thoroughly decomposed— a large volume of gas is formed as well, 
and the milk-sugar is converted into carbon dioxide, hydrogen and 
lactic acid.^ The alkaline products of putrefaction formed by B. 
mesentericus neutralize, to a large degree, the acid products formed by 
B. coli and the net change in the chemical composition of the milk is 
much greater than the sum of their separate activities. 
Abnormal bacterial fermentations of milk are occasionally sources 
of great trouble to dairymen. One of the more common of these is 
kno^^Tl as ropy or slimy milk, in consequence of the viscidity which 
develops. Several kinds of bacteria cause ropiness, but of these 
B. lactis viscosus appears to be more frequently concerned. A bitter 
flavor may be imparterl to milk either from the feed of the cow or by 
the growth of bacteria. The latter is usually due to the partial diges- 
ti(m of the milk proteins resulting in an accumulation of peptones. 
The gas bacillus— B. aerogenes capsulatus— produces an energetic 
fermentation of milk-sugar. The spores of the organism are very resist- 
ant to physical agents and are often found in commercial grades of 
lactose, which is prepared from milk. There is evidence that this 
organism, transmitted through milk, may incite mild or severe diarrhea 
in children, less frequently in adults. Pasteurized milk, particularly 
that originating in unclean dairies, occasionally contains considerable 
numbers of gas bacilli and the absence of lactic-acid-forming bacteria 
in such milk (which normally restrain their activity) may be a factor in 
its ability to develop rapidily. 
Proteolytic bacteria, particularly spore-forming varieties of the 
Subtilis-lNIesentericus Group, decompose milk proteins with the forma- 
tion of casein peptones or even polypeptids. They occasionally mul- 
tiply rapidly in pasteurized milk, when the degree of heat applied has 
been sufficient to kill the lactic-acid-producing bacteria; ordinarily 
lactic acid restrains the growth of proteolytic bacteria. 
Pathogenic bacteria, as a rule, produce very little change in the 
appearance of milk and the chemical compositicm also is not greatly 
altered during their development.- Ordinarily it is impracticable to 
search for pathogenic bacteria in this medium, for the chances of 
success are minimal. 
Milk in Its Relation to the Public Health. —The importance of 
milk as a medium for the transmission of pathogenic bacteria is shown 
in the following list transcribed from the compilation of Trask.^ 
1 Kendall: Boston Med. and Surg. Jour., 1910, 163, 322. 
- Kendall, Day and Walker: .Jour. Am. Chem. Soc, 1914, 36, 1937-1966. 
2 Bulletin 41 of the Hygienic Laboratory, Washington, D. C, January, 1908. 
44 
