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. 



