SIGNIFICANCE OF COLON COUNT IN MILK. 5 
were plated on litmus-lactose-asparagin agar of the following com- 
position : 
Per cent. 
Agar 1. 5 
Asparagin 0. 3 
Lactose 1.0 
Sodium dibasic phosphate 0. 1 
Saturated neutral solution of litmus 2. 
From these plates typical colonies of the colon-aerogenes group 
were then picked and inoculated into the dextrose-peptone broth 
of Clark and Lubs 3 , and the methyl-red test made after five days as 
proposed by the same authors. By means of this test organisms 
are divided into B. coli and B. aerogenes types. If the proportion of 
the types changed as the feces dried, then enrichment in milk should 
show the presence of the B. aerogenes type. It is evident from Table 
1, where the percentage of the two types after enrichment is shown, 
that the general proportion of B. coli to B. aerogenes which exists in 
fresh feces is not changed to any great extent as the feces dries. It 
is interesting to note, however, that when the feces was seven days 
old the enrichment method showed the presence of as high as 1 1 per 
cent of the B. aerogenes type. They were still present on the tenth day 
but not on the fourteenth, in milk held both at 70° F. (21.1° C.) and 
at 86° F. (30° C). This indicates that as feces dries the proportion 
of B. aerogenes to B. coli in it may increase slightly, but, generally 
speaking, it is not believed that this is the main source of the B. 
aerogenes type. 
Table 1. — Effect of drying cow feces on the proportion of Bacillus coli and B. aerogenes 
types. 
Number of 
days dried 
at 70° F. 
(21.1° C). 
Held 24 hours at 70° F. (21.1° C). 
Held 24 hours at 86° F. (30° C). 
Colon 
count. 
B. coli. 
B. aero- 
genes. 
Colon count. 
B. coli. 
B. aero- 
genes. 
(fresh).. 
1 
Per c. c. 
320, 000 
2, 500, 000 
420, 000 
760, 000 
490, 000 
680, 000 
6, 500, 000 
6, 500, 000 
Per cent. 
100 
100 
100 
100 
100 
89 
99 
100 
Per cent. 





11 
1 

Per c. c. 
26,000,000 
23,000,000 
103, 000, 000 
210,000,000 
280.000,000 
132,000,000 
270, 000, 000 
37,000,000 
Per cent. 
100 
100 
100 
100 
100 
99 
96 
100 
Per cent. 





1 
4 

2 
3 
6 
7 ... 
10 
14 
The colon-aerogenes group of organisms is introduced into milk 
not only through feces but also from unsterilized utensils. In fact 
this is a very important source of contamination. Both B. coli and 
B. aerogenes types can be introduced into milk from unsterilized 
milk utensils, as may be seen in Table 2. The results given in 
the table represent a very extreme condition of production, such as 
