18 BULLETIN 739, U. S. DEPARTMENT OF AGRICULTURE. 
colon-aerogenes group which can be introduced into milk under 
normal conditions of production, it will be of great importance in 
connection with the significance of the colon count. If correct, it 
means that any colon count over 2,000 per cubic centimeter could at 
once be attributed to growth. 
The results obtained in our experiments indicate that, generally 
speaking, 2,000 per cubic centimeter is the maximum number of organ- 
isms of the colon-aerogenes group introduced into fresh milk. It is* 
realized, however, that occasionally abnormal conditions may be en- 
countered where the colon count in fresh milk runs higher than the 
maximum limit mentioned. The only time such a condition was met 
in the experiments occurred during the period from August 21 to Sep- 
tember 12, 1917, when milk was produced under the dirty conditions as 
previously described. The utensils were held for 24 hours before 
washing, and then simply washed in lukewarm water without brush 
or washing powder. During this 24-hour period the air temperature 
ranged from 70° F. (21.1° C.) to 98° F. (36.7° C), a very favorable 
condition for growth of organisms of the colon-aerogenes group in the 
unwashed utensils. Table 10 shows that the colon count of 12 samples 
of fresh milk produced under these conditions ranged from 80,000 
to 6,700,000 per cubic centimeter. The experiment was stopped 
on September 12 and was repeated about October 1 under the same 
conditions with the exception that the air temperature averaged 
much lower, ranging between 40° F. (4.4° C.) and 70° F. (21.1° C). 
It was found that at this time the colon counts were all within the 
maximum of 2,000 per cubic centimeter. This led to the belief 
that the holding of utensils containing milk drainings at the high 
temperatures which prevailed during the period from August 21 to 
September 12 was responsible for the extremely heavy contamina- 
tion by organisms of the colon-aerogenes group. 
In order to confirm this opinion further experiments were con- 
ducted during October under the same dirty-barn conditions except 
that the utensils, which were not washed for 24 hours, were held in 
artificially heated rooms. From the results in the lower part of Table 
10 it is evident that even under these conditions it was impossible to 
obtain the high colon counts that had previously been obtained. 
While it was impossible to maintain as high temperatures artificially 
as occurred normally in our earlier experiment, temperatures as high 
as 86° F. (30° C.) were obtained, and it is believed that in many cases 
the utensils were held at as high temperature as in the previous 
experiment. In the last experiment where the utensils were held 
in artificially heated rooms Ihe colon count ranged from 100 to 
350,000 per cubic centimeter. Only 9 of the 25 samples showed 
more than 2,000 organisms of the colon-aerogenes group per cubic 
centimeter. 
