eet ay 
MILK PRESERVED AT SEVENTY AND FIFTY DEGREES. 45. 
At all events, the conclusion from these facts is that the 
straining of milk through cheese cloth, while it removes a con- 
siderable portion of the dirt, has no considerable influence upon 
the number of bacteria present. 
2. Liffect of straining upon the acid bacteria compared with 
the non-acid species.—'The effect previously mentioned, that cen- 
trifugalized or strained milk frequently sours quicker than milk 
not thus treated, suggested that possibly the straining removed 
a larger number of the non-acid bacteria, leaving in the milk 
the acid bacteria in greater proportion. This might explain 
their somewhat more rapid growth and the quicker curdling. 
To test this conclusion we have made a determination of the 
number of acid bacteria in the four samples of milk before and 
after straining, and also a determination of the number of non- | 
acids. At the same time a separate determination of the lique- 
fying bacteria was made. The second, third, and fourth columns 
in the tables give the results. It will be seen that there is a: 
great variation in the number of acid bacteria found in milk 
from day to day, even samples from the same cow showing 
wide differences. For example, on Jan. 16, in Table 4, we find 
that the milk contained 316 acid bacteria per cubic centimeter, 
while on Jan. 11 there were 3,250. Taking tests close together, 
the differences were also great. On Jan. 7, Table 4, we find 
833 acid bacteria, while two days later there were 1,312, and 
two days later still, 3,250. The per cent. of acid bacteria 
which was removed by straining was smaller than the total per 
cent. of bacteria removed, in the samples given in Tables 3 and 
54 while in Tables 5 and 6 this relation was reversed. If, how- 
ever, we compare the percentage of acid bacteria in strained and 
unstrained samples in all four tables, it will be seen that in the 
majority of cases (ten samples against seven) the strained milk 
contained a higher per cent. of acid bacteria than did the same. 
milk before straining, although the average of the whole showed 
little difference. This fact suggests at first sight that the non- 
acid bacteria are more likely to be removed by straining than 
the acid producing organisms, a fact further confirmed by the 
_ work upon aseptic milking described on a later page, and that 
possibly here may be the explanation of the more rapid curdling 
of such samples. 
