SIGNIFICANCE OP COLON COUNT IN MILK. 



•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 11 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 e. 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 



