20 BULLETIN 739, U. S. DEPARTMENT OF AGRICULTURE. 
tamination during production. Jackson (6) evidently believed that 
these organisms did not grow in milk, for he states: 
Contrary to expectation it has been found that under ordinary conditions, consider- 
able numbers of other bacteria being present, B. coli does not increase in milk, or if so 
only to a very slight extent, then gradually dies out. On this account the amount of 
original contamination may be determined. 
Most investigators, however, have recognized the fact that organ- 
isms of the colon-aerogenes group were able to multiply in milk 
and that this fact complicated the significance of the colon count. 
Kinyoun (9), while recognizing that the age of the milk and the 
temperature at which it has been held are important, believed that 
original contamination was responsible for the most part in causing 
high colon counts. According to Prescott (12), organisms of the 
colon group will grow in milk which is held at 50° F. (10° C-), and 
he found that even when milk was packed in ice for several days 
the rate of increase was much greater than had been expected. 
This author believes that the question of growth must be taken 
into consideration in interpreting the colon count, for he says: 
The mere question of the numbers of colon bacilli found in milk or cream may be 
settled or explained in two ways. It may have been due to initial infection or due 
to growth. Here discrimination must be employed as to the relative number of 
organisms and the types which are present in order to determine which of these 
explanations is the satisfactory one. 
The opinion of Race (13) on this subject is expressed in the following 
statement : 
"When milk is kept at a temperature not exceeding 45° F. (7.2° C.) the B. coli do 
not increase and this temperature may therefore be regarded as the critical anabolic 
temperature. Above this point they rapidly multiply and in summer the B. coli 
content of milk must be regarded as due more to reproduction than original con- 
tamination. 
In the several pages following are shown the results of a large 
number of samples of milk produced under different barn con- 
ditions and the growth of organisms of the colon-aerogenes group 
at various temperatures. Of these, 20 samples were produced 
under clean conditions and handled in sterilized utensils, 34 samples 
were produced under dirty conditions with sterilized utensils, and 
23 samples were produced under similar dirty conditions but handled 
in unsterilized utensils, and in each case the samples were held at 
50° F. (10° C.) and duplicate samples were held at 60° F. (15.6° C), 
and the colon count determined in the milk when fresh and after each 
succeeding 24 hours up to 96 hours. The results obtained when the 
milk was held at 50° F. (10° C.) are shown in Table 11. The results 
have been summarized and the per cent of samples showing the 
presence of organisms of the colon-aerogenes group in 1/100 of a 
