84 STORRS AGRICULTURAL EXPERIMENT STATION. 
EXPERIMENTS WITH DIFFERENT CULTURE MEDIA. 
To determine the best culture medium required a longer 
series of experiments. Three different culture media were 
used in comparative tests, made as follows: 
Milk whey culture media.—To about two liters of milk there 
is added enough rennet to curdle the milk in about half an 
hour. After a thorough curdling the curd is cut to pieces with 
a knife to allow the whey to exude, and the whole is then 
strained through a cheese cloth. The whey thus pressed 
from the curd is placed in a flask and sterilized in an autoclav 
for forty minutes at a pressure of 5 pounds. ‘This sterilization 
is for the purpose of destroying the resisting spores, which are 
very likely to be present in the milk. After sterilization the 
whey is filtered through filter paper, and should be clear. There 
is then added to it 1334 per cent. of gelatin. The material is 
then dissolved by a moderate heat, neutralized to the phenol- 
phthalein by titrating and adding NaOH in the ordinary way. 
After neutralization the reaction is brought to 1.5 per cent. 
acid by adding 15 cubic centimeters of normal hydrochloric 
acid for each liter of the material. The white of an egg is 
added, the whole is boiled briskly for a few moments, the water 
of evaporation replaced (by weight), and the mixture filtered 
through absorbent cotton. The filtered solution is placed in 
test tubes, each containing exactly 8 cubic centimeters, and then 
is sterilized in steam upon three successive days in the usual 
manner. | 
A slight modification of the above has been commonly adopted. 
Where the gelatin is subsequently used, there is added to it con- 
siderable water (with the litmus solution and milk dilution), 
and this dilutes the food ingredients of the whey more than is 
desirable. ‘To avoid this we proceed as follows: ‘The sterilized 
milk whey is neutralized, and 1o per cent. gelatin added to it 
with the white of an egg. It is then cooked until 27 per cent. 
of its weight has evaporated, after which it is brought to the 
desired grade of acidity and filtered without replacing the water 
of evaporation. ‘This water is subsequently replaced with the 
litmus solution and the diluted milk, as described below, giving 
a final solution of the desired strength. 

