SIGNIFICANCE OF COLON COUNT IN MILK. 6 
If the colon count were a direct measure of original contamination 
during milking, it would be a most valuable aid in determining the 
purity of a milk supply. Can the colon count, however, be consid- 
ered a direct measure of such contamination? This is a question 
which seems to be unsettled. As has been shown there are opinions 
on both sides of the question. While the test was formerly considered 
of considerable importance, more recently it has lost some of its sig- 
nificance because of the recognized ability of organisms of the colon 
and aerogenes group to grow rapidly in milk when not properly cooled 
and kept cold. 
A test which gives promise of indicating original contamination, 
particularly fecal contamination, is worthy of attention, and it has 
seemed desirable to study this subject under controlled conditions 
with a view of determining the true value of the colon count in milk. 
Throughout this paper the expressions " colon- aerogenes group" 
and " colon count" are used. The "colon count" means the number 
of organisms belonging to the colon-aerogenes group, and the term 
" colon-aerogenes group" as used includes both the Bacillus coli and 
B. aerogenes types of organisms. When any differentiation is made 
between the B.coli and B. aerogenes types it will be indicated in the 
text. 
DO ORGANISMS OF THE COLON-AEROGENES GROUP INDICATE THE 
PRESENCE OF MANURE IN FRESH MILK? 
If the organisms of the colon-aerogenes group are to be considered 
evidence of external contamination it must first be known whether 
or not they are present in the udders of cows. Both Savage (17) and 
Race (13) believe that organisms of this group are derived from 
sources outside the udder. Our results confirm this opinion, for in 
an examination of four cows no organisms of the colon-aerogenes 
group were ever found in milk drawn directly from the teats into 
sterile tubes. While only a few cows were examined, the results 
obtained, together with those of other investigators, seem to indicate 
that in general organisms of the colon-aerogenes group are not de- 
rived from the udder of the cow and therefore represent external 
contamination. 
Raw market milk contains both the Bacillus coli and B. aerogenes 
types of organisms, as has been shown by the work of Rogers, Clark, 
and Evans (14)., who found the colon-aerogenes group in such milk 
to be made up of nearly equal proportions of B. coli and B. aerogenes 
types. This being the case, it becomes necessary to know the source 
or sources of the B. coli and B. aerogenes types before they can be 
^accepted as an indication of manurial contamination. It has been 
known for a long time that cow manure contains large numbers of 
organisms of the colon-aerogenes group, and the authors last men 
