BACTERIA IN THE DAIRY. 47 
The cultures used for ripening were made as follows: Skimmed 
milk was placed either in large test tubes or in Erlenmeyer flasks 
and sterilized by steam on four or five successive days, an abso- 
lute sterilization being thus obtained. The amount of the milk 
in each flask was varied in the different experiments for the pur- 
pose of determining the most convenient quantity to use. It 
was found as the result of many experiments that the best 
quantity was about one-thirtieth of the amount of cream to be 
inoculated, bulk for bulk. After sterilization the milk was 
inoculated with a loop full of a pure culture of the organisms to 
be tested, obtained from agar tubes. The inoculated milk was 
then allowed to grow for a varying length of time at varying 
temperatures, the variations in time and temperature being for 
the purpose of determining the best conditions under which the 
growth should occur. There were thus obtained milk cultures 
of the species to be experimented upon whose age was from one 
to fourteen days or more. A culture of about two days was 
found to be most satisfactory. 
The cream ripening was conducted as follows: After the pas- 
teurization of the cream as above described, it was cooled to a tem- 
perature of 30° C. (86°F.) or lower, and the milk culture was poured 
into it. The milk can was then closed to prevent the entrance of 
dust, either by closing the can with its proper cover, or by filling 
it with a plug of cotton, and the cream was set aside to ripen. 
In the various experiments the ripening was carried on at three 
different temperatures, the temperatures chosen being 37°, 27°, 
and 20°C. (99°, 81° and 68°F.) The experiments also varied as 
to the length of the ripening, in some cases the ripening being 
allowed to continue for twenty-four hours at the above men- 
tioned temperatures, and at others for forty-eight hours. During 
the ripening the cream was occasionally shaken to produce as 
thorough contact with oxygen as possible and thus to imitate 
closely the conditions in the vat of the ordinary creamery. 
The temperatures used in ripening are all higher than those usu- 
ally used in creameries. But this was found to be advantageous 
in ourwork. The cream could be ripened for forty-eight hours at 
20°C, (68°F.) and not be over-ripened, and even the temperature of 
27°C, (81°F.) did not injure the cream in twenty-four hours ripening. 
Such temperatures would have over-ripened cream as ordinarily 
collected for creameries. ‘The probable explanation is as follows: 
1. Our cream was probably not as highly inoculated with bacteria 
