12 
BULLETIN 139, U. S. DEPARTMENT OF AGRICULTURE. 
HOW MANY ORGANISMS OF THE COLON-AEROGENES GROUP CAN BE 
INTRODUCED INTO MILK DURING MILKING? 
In order to interpret the significance of the colon count it is neces- 
sary to know not only that organisms of the colon-aerogenes group 
are always introduced into milk, but also in what numbers under 
both normal and abnormal conditions. In determining the numbers, 
the colon count has been made on a great many samples produced 
under different conditions. The results of these examinations have 
been summarized and are presented in Table 7. They are discussed 
briefly at this point in order to emphasize the fact that under normal 
conditions small numbers of organisms of the colon-aerogenes group 
are found in fresh milk. The averages given for the colon-aerogenes 
group are based on those samples showing the presence of colon 
bacilli in 1/100 of a cubic centimeter. Included in the table are the 
results of the examination of 14 samples of certified milk, which were 
examined at the time of delivery to the consumer. Except for the 
certified milk all the data presented in the table are based on the 
examination of milk produced under controlled conditions from 4 
cows kept in a small experimental barn. The condition of the barn 
and the cows was changed at times from clean to extremely dirty 
in order to suit the purpose of the experiments. The handling of 
the utensils was also varied for similar reasons. 
Table 7. — Summary of colon-aerogenes contamination under different conditions of 
milk production. 
Conditions of milk production. 
Samples 
exam- 
ined. 
Colon-aerogenes 
organisms in 
1/100 c. c. 
Range of 
colon 
counts. 
Average 
colon 
count. 
Number. 
14 
Number. 
i 
Per cent. 

Per c. c. 
1-20 
Per c. c. 

86 
6 
6.9 
100-200 
116 
56 
6 
10.7 
100-400 
183 
84 
24 
28.6 
( 2 ) 
( 3 ) 
28 
20 
71.4 
100-1, soo 
750 
Average 
total 
bacteria. 
Certified milk as delivered 
Clean barn, clean cows, sterilized uten- 
sils (A) 
Dirty barn, dirty cows, utensils ster- 
ilized (B) 
Dirty barn, dirty cows, utensils washed 
at once after milking, but not sterilized 
(C) 
Dirty barn, dirty cows, utensils held 
for 8 hours before washinc, and not 
sterilized (D) 
Per c. c. 
10, 471 
6,091 
36, 541 
465,086 
1,299,000 
1 7+ in 1 cubic centimeter. 
2 23 samples, 100-2,000. 1 sample, 28, 100. 
3 Average of 23 samples, 557. Average of 24 samples, 1,717. 
The examination of 86 samples of milk produced in a clean barn, 
from clean cows, and with sterilized utensils, is shown in Table 7. 
The term " sterilized" signifies steamed for 20 to 30 minutes. That 
the milk produced under these conditions was of high quality from a 
bacterial standpoint is shown by the average total count of 6,091 per 
cubic centimeter. Only 6 samples of the 86, or 6.9 per cent, con- 
tained organisms of the colon-aerogenes group in 1/100 of a cubic cen- 
timeter. The number of these organisms in the 6 samples ranged 
from 100 to 200 and averaged 116 per cubic centimeter. 
