SIGNIFICANCE OF COLON COUNT IN MILK. 31 
HAS THE COLON COUNT ANY SIGNIFICANCE IN RAW MILK? 
Before discussing the question of whether the colon count in raw 
milk has any significance it must be pointed out that the colon count 
as made at present includes both B. coli and B. aerogenes types, of 
which the B. coli type is principally of fecal origin and the B. aero- 
genes type mainly of nonfecal origin. If, therefore, it could be 
assumed that the number of organisms of the B. coli type was a direct 
measure of the amount of manure in milk (an impossible assumption), 
the colon count would not even then be a direct measure of such 
contamination, since it may include the B. aerogenes type. Since, 
however, it is impossible at present to differentiate between the two 
types by plating methods alone, the significance of the colon count 
must be considered as it stands, irrespective of the fact that it 
measures the number of both types of organisms. 
The significance of the colon count must be considered in two 
distinct relations; first, in its connection with fresh milk and, second, 
in its connection with milk which has been held. 
SIGNIFICANCE IN FRESH MILK. 
The colon count is, generally speaking, a measure of contamination 
during production only when fresh milk (less than two hours old) is 
examined. In fresh milk the colon count measures the degree of 
contamination from several sources. The organisms gain entrance 
directly from manure, from unsterilized utensils, and in small num- 
bers from the air and from other minor sources. 
Milk produced under clean conditions and handled in sterilized 
utensils usually does not show the presence of organisms of the 
colon-aerogenes group in ^ of a cubic centimeter, and probably they 
are not present in even larger quantities. In milk produced under 
dirty-barn conditions and handled in unsterilized utensils these 
organisms can usually be found in ^ of a cubic centimeter and may 
run as high as 2,000 per cubic centimeter. The colon count of fresh 
milk therefore bears a somewhat direct relation to the conditions 
under which the milk was produced. A similar relation, however, 
does not exist between the colon count and the amount of manurial 
contamination, first, because different samples of feces vary widely 
in their colon content, and, secondly, because these organisms may 
be introduced into milk through other channels, particularly from 
unsterilized utensils. 
SIGNIFICANCE IN MILK THAT HAS BEEN HELD. 
When milk is not fresh, no significance can be attached to the colon 
count in relation to contamination during milking unless it is known 
that the milk is comparatively fresh and that it has been kept at 
temperatures not exceeding 50°* F. (10° C). Perhaps a safer limit 
