SIGNIFICANCE OF COL.ON COUNT IN MILK. \) 
B. coli type is concerned except for infection from manure and uten- 
sils, all other avenues of infection are probably of a negligible nature. 
The B. aerogenes type does not indicate direct fecal contamination, 
because it is found only occasionally in manure and then only in an 
extremely small proportion in comparison with the B. coli type. On 
the other hand, the presence of the B. aerogenes type may indicate 
indirect fecal contamination through unsterilized utensils. As has 
been previously shown, this type of organism may be introduced 
through unsterilized utensils which have been held for 24 hours 
before washing in lukewarm water without a brush. Under this 
condition large numbers of the colon- aerogenes group were intro- 
duced which were principally of the B. aerogenes type. This can be 
explained only by the growth of organisms of the colon-aerogenes 
group in the utensils during storage following the original infection 
with the B. aerogenes type, which in all probability was due to either 
fecal or air contamination. If due to air contamination, the B. 
aerogenes type was very likely of nonfecal origin. The abnormality of 
this condition of production and the lack of sufficient results under 
normal conditions prevent a statement as to the probability of the 
contamination of milk by the B. aerogenes type through unsterile 
utensils. Air-borne infection probably plays a very important part 
in the introduction of this type in small numbers into milk, such con- 
tamination originating mainly in various feeds and in the soil. It 
seems evident, therefore, that the B. coli type in fresh milk indicates 
fecal contamination either directly or indirectly, while the B. aerogenes 
type occasionally may indicate indirect fecal contamination, but is 
usually an index of nonfecal contamination. 
Although the B. coli type of organism may be considered an index 
of fecal contamination in fresh milk, it must be remembered that the 
colon count as usually made and as considered in this paper includes 
both types and does not differentiate between them. Our results 
confirm the opinion of Rogers, Clark, and Evans (16), who state: 
It is difficult to avoid the conclusion that while the presence of fecal bacteria in 
milk may be determined with great certainty, the ordinary presumptive tests and 
even the usual confirmatory tests do not necessarily prove the contamination of the 
milk with fecal matter. In order, therefore, to prove definitely the presence of the 
fecal colon type special confirmatory tests must be used to determine their presence. 
CAN MILK BE PRODUCED COMMERCIALLY WITHOUT CONTAMINA- 
TION BY ORGANISMS OF THE COLON-AEROGENES GROUP? 
This is a very important question, for if milk can be produced and 
handled under clean conditions without contamination by organisms 
of the colon-aerogenes group. the presence of these organisms at any 
time in the milk would prove that it had not been so produced and 
handled. 
75649°— 18— Bull. 739 2 
