Frost—Bacteriological Control of Public Milk Supplies. 1345 
The percentages obtained are plotted as ordinates, and the days 
as abscissae. In this way it will be found that the curves formed 
will fall below the diagonal, formed by drawing a line from 0 to 
100%, on the last day in the case of pasteurized or certified milks, 
and that the curve will rise well above this diagonal in the case 
of raw or highly contaminated milks. It has not been possible 
so far to obtain similar results using a 37° C. temperature. 
2. Gas Production in Lactose Media. (Table VII.) The 
Milk Commission, # states * 4 pasteurized milk should not contain 
colon bacilli in 1 c. c. as determined by cultural methods.” In 
some cities this criterion is being applied, as for example, in Wash¬ 
ington, I). C. This organism has served a most useful purpose in 
water analysis, and there seems every reason to believe that tests 
for it may be of great service in milk work. Clean milk, as it 
exists in the udder of the cow, does not contain B. coli or other 
bacteria capable of fermenting lactose with gas production. 
Ayres and Johnsonf find anaerobic bacteria in pasteurized milk 
which produce gas and which might be mistaken for B. coli in 
preliminary tests. If they are found in the milk after it is 
drawn, they must come from outside sources, and these must 
be the manure, the persons handling the milk, or the utensils with 
which the milk comes in contact. 
The cleanliness: of a milk could, in reality, be measured by 
the relative abundance of bacteria capable of producing gas in 
a lactose medium, or in other words, by the relative abundance 
of B. coli and its allies. 
As to the cultural methods it seems likely that those employed 
for water will be found 1 equally satisfactory for milk. Lactose 
peptone bile in fermentation tubes has been uniformly used! in 
all analyses reported here. In a considerable number of in¬ 
stances a special medium neutral red milk broth, has also been 
used. An attempt too has been made to use Endo’s medium. 
The methods or preparation of these media has already been 
considered, and the results obtained by their use are alone to be 
discussed here. 
Some attempt was made to identify the organisms producing 
gas in the lactose media as B. coli by isolating in pure culture in 
lactose litmus agar, and then running through the fermentation 
* Loc. cit. 
t U. S. Dep’t of Agr. Bu. An. Ind., Bull. 161, 1913, p. 60. 
