22 BULLETIN. 739', U. S. DEPARTMENT OF AGRICULTURE. 
colon-aerogenes group, and this one contained 3,200. After the 
milk had been held 72 hours, 83.3 per cent were still negative in 
1/100 cubic centimeters while 16.7 per cent were positive. The 
colon count ranged from 1,600 to 28,000, the average being 10,533 
per cubic centimeter. After 96 hours at 50° F. (10° C.) the same 
percentage of the samples showed growth as after 72 hours, but the 
average colon count was higher. 
Among the 34 samples of milk produced under dirty conditions 
and handled in sterilized utensils 5.9 per cent showed organisms 
of the colon-aerogenes group in 1/100 of a cubic centimeter of milk. 
The range in colon count was from 100 to 300 and the average 200 
per cubic centimeter. After 24 hours at 50° F. (10° C.) none of 
the samples showed the organisms in 1/100 of a cubic centimeter. 
This is explained by the fact that the colon count in the samples 
which showed positive results in the fresh milk ranged from 100 to 
300. Since 1/100 of a cubic centimeter of milk was plated this 
meant from one to three colonies per plate, and as there was prob- 
ably no growth during the 24-hour holding period at 50° F. (10° C), 
these organisms were missed in a hundredth dilution on the second 
day's plating. At the end of 72 hours only 4.4 per cent of the 
samples showed colon-aerogenes organisms, which averaged 3,200 
per cubic centimeter. There was a slight growth among these 
samples between 72 and 96 hours, for, as may be noted in the 
table, 45.8 per cent showed positive results at the end of 96 hours. 
The colon counts ranged from 2,000 to 186,000 and averaged 24,172 
per cubic centimeter. The results obtained in the examination of 
23 samples produced under dirty conditions and handled in un- 
sterilized utensils agreed very closely with those just discussed. 
From these results it seems evident that there is practically no 
growth of organisms of the colon-aerogenes group in milk produced 
under normal conditions when it is held for a period of 48 hours at 
50° F. (10° C). After 72 hours at this temperature there was 
evidence of multiplication, which was still further increased by 
holding for 96 hours. 
Duplicate samples of the milk produced under the conditions pre- 
sented in Table 11 were held at 60° F. (15.6° C.) and the summarized 
results are given in Table 12. It will be noted that there is a marked 
difference in the growth of the organisms of the colon-aerogenes 
group in milk held at the higher temperature. Quite high colon 
counts were obtained in the majority of samples held at 60° F. (15.6° 
C.) even in 24 hours. No further discussion of the results is neces- 
sary, as the effect of temperature on the colon count is plainly shown 
by the results presented. 
