COMPARISON OF BACTERIA IN MILK. 33 
COMPARISON OF BACTERIA IN STRAINED AND 
UNSTRAINED SAMPLES OF MILK. 
H. W. CONN AND W. A. STOCKING, JR. 
——- ee ——_ 
In the experiments described in the last annual report, it was 
noted that milk which had been strained or had passed through 
a centrifugal, although containing smaller numbers of bacteria 
than the milk that had not been so treated, quite frequently 
soured and curdled quicker than the normal milk. ‘The first 
series of experiments here reported was designed for the pur- 
pose of testing somewhat carefully the effect of straining milk | 
upon the number of bacteria and upon the keeping property of | 
the milk. The method of experimenting was as follows: 
Milk was drawn from individual cows in an ordinary open 
pail, and after the cows were completely milked a sample of the 
milk was obtained. ‘The milk was then strained through two 
layers of sterilized cheese cloth, and a second sample obtained 
in the same way. Both samples were taken to the laboratory, 
and four plates in litmus gelatin made from them immediately. 
Both were then placed at a temperature of 70°, and after 50 
hours a second series of plates was made, and the amount of 
acid present in the milk was determined. The milk was then 
left at the same temperature until the time of curdling, at 
’ which time d third series of plates was made, and a third test 
of the amount of acid. In some experiments the milk curdled 
during the night, and this last series of tests could not be made. 
In all cases at least four plates were made, and the results 
tabulated represent an average of the samples. In studying 
the plates after proper growth, the total number of bacteria was 
determined, the number of lactic organisms as indicated by the 
production of acid in litmus gelatin, and the number of pepton- 
izing forms as indicated by the liquefaction of the gelatin. The 
results were determined both in numbers and in percentages. 
The following table represents the results of this series of 
experiments. 
