32 BULLETIN 739, U. S. DEPARTMENT OF AGRICULTURE. 
would be 45° F. (7.2° C). In other words, if the history of the milk 
is not known it is impossible to interpret the colon count in terms of 
the condition under which it was produced. This situation arises 
because of the fact that organisms of the colon-aerogenes group grow 
rapidly in milk when it is held above 50° F. (10° C). 
When the history of the milk is not known, it is believed that colon 
counts above 2,000 per cubic centimeter indicate growth. This 
belief is based on the fact that only one sample of fresh milk out of 
the 254 samples which were produced under conditions ranging from 
clean to extremely filthy contained more than 2,000 colon per cubic 
centimeter. If, therefore, a sample of milk of unknown history is 
examined and found to have a colon count between 100 and 2,000 
per cubic centimeter, it is impossible to decide whether the colon 
count indicates original contamination or whether this small number 
of organisms was due to the growth of the few originally introduced 
into a very clean milk. Colon counts above 2,000, however, under 
normal conditions can be attributed to growth. In this connection 
the colon count is significant so far as it indicates that the milk has at 
some period in its history been held above 50° F. (10° C). 
There is one abnormal condition of production under which 
fresh milk may have a high colon count. As previously pointed 
out, in one series of experiments where utensils were allowed to 
contain milk drainings for 24 hours during extremely hot weather, 
and then washed carelessly in lukewarm water without the use of 
brush or washing powder, the colon count of the fresh milk averaged 
about 1,000,000 per cubic centimeter. An attempt was made to 
duplicate these counts under similar conditions, but without success. 
It is believed that this extreme condition of production would rarely 
be encountered in the commercial production of milk. High colon 
counts due to this condition can probably be readily distinguished 
from similarly high colon counts which are due to growth, because 
the ratio of total count to colon count would probably be less than 
1 to 50 in the fresh milk, while in that due to growth the ratio would 
be much higher. 
SUMMARY. 
1. The colon count as determined at the present time includes both 
the B. coli and B. aerogenes types of organisms. Since the B. coli 
type is principally of fecal and the B. aerogenes type of nonfecal 
origin, the colon count at best can not be a direct measure of ma- 
nurial contamination. 
2. Fresh milk produced under the best conditions always contains 
some organisms of the colon-aerogenes group, but rarely contains 
over 2,000 per cubic centimeter even when produced under the worst 
conditions normallv encountered. , 
