86 STORRS AGRICULTURAL EXPERIMENT STATION. 
more dry litmus in making the litmus solution, using a sufh- 
cient amount of litmus to make a solution deep enough to give 
the desired blue when mixed.with the gelatin in the above pro- 
portions. A few tests with each lot of litmus purchased makes 
it possible to obtain always the same depth of blue when it is 
mixed with gelatin in proportions of 2 cubic centimeters to 8 
cubic centimeters. 3 : 
After the ditmus is mixed with the gelatin, one cubic centi- 
meter of the diluted milk to be tested is added to each tube, 
reducing the gelatin mixture to ro per cent. ‘The whole is 
thoroughly mixed, poured into petri plates, and allowed to 
harden. The plates are cultivated at 70° for six to seven days, 
if possible, before final study, and the final study is made with 
a hand lens and a compound microscope, using a 1% inch 
objective. 
COMPARATIVE EXPERIMENTS. 
In testing the efficiency of different culture media it is neces-_ 
sary to have in mind that there are two points to be determined. 
1. The value of. the medium in determining the umber of 
bacteria present in milk. For this purpose the medium which 
gives the highest count will be undoubtedly the best. 2. The 
value of the medium in dzfferentiating the species of bacteria. 
The chief object of our experiments has been to determine not 
the total number of bacteria, which we regard as of compara- 
tively little importance in milk, but the proportions of the 
_ different species of bacteria present in milk under different cir- 
cumstances. For this reason, therefore, the matter of the dif- 
ferentiation of species is of much more significance than the 
matter of the total number of bacteria. In testing the culture 
media, therefore, more emphasis must be placed upon the 
successful differentiation of species than upon the detection of 
total numbers. | 
GRADE OF ACIDITY. 
This was tested by making culture media of different grades 
of acidity and testing them by comparative experiments with 
the satne lot of cream. Briefly the results were as follows: A 
solution neutral to phenol-phthalein or one with a reaction of 
.5 per cent. acid was unsatisfactory, the numbers of colonies 

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