82 STORRS AGRICULTURAL EXPERIMENT STATION. 

that the typical milk bacteria would be more likely to develop 
vigorously in solutions containing milk than in a,medium made 
up as the ordinary culture medium is. ‘To determine, there- 
fore, whether it was not possible to improve the methods of 
study, a long series of experiments was begun to test a num- 
ber of culture media under a variety of conditions. 
MODIFICATION OF CULTURE MEDIA. 
After some trials we finally adopted a new method of mixing 
litmus with the gelatin, which has done away completely with 
the irregularities of the earlier medium. In our earlier method 
we mixed the litmus solution with the peptone gelatin, etc., 
when the medium was prepared, giving a blue mixture diffi- 
cult to neutralize and lacking in uniformity. We now keep 
the litmus solution totally separate from the gelatin until the 
time of using. 
The details of our method of preparing the litmus solution 
are as follows: 
Fifty grams of dry litmus cubes are mixed with 300 cubic 
centimeters of water. This mixture is allowed to steep for a few 
hours at about 70°C., or soaked for 24 hours at the ordinary 
room temperature, for the purpose of dissolving the active 
material from the litmus. ‘The solution is then filtered, giving 
a deep blue solution. ‘This material is always alkaline to lit- 
mus, as shown by its deep blue color, but it is found to be acid 
to the phenol-phthalein test. In order to use it, the litmus 
solution must be brought to the same grade of alkalinity that 
is desired for the final culture media (1.5 per cent. acid to 
phenol-phthalein). ‘To do this, it is necessary first to deter- 
mine the exact reaction of the litmus solution. Five cubic 
centimeters of this solution is placed in an evaporating dish 
and diluted with 45 cubic centimeters of water. ‘This is titra- 
ted with 449 normal hydrochloric acid until the Ztmus neutral 
point is reached, the point being recognized by the turning of 
the color into a faint red. The reading upon the burette will 
of course show how much 149 HCl is needed to bring 5 cubic 
centimeters of the litmus solution to the litmus neutral point. 
An average of three tests is needed, and the amount of normal 
HCl necessary to bring the whole litmus solution to the litmus 
neutral point is determined by calculation. This amount of 
HCl is added to the solution. 

