QUALITATIVE ANALYSIS OF MARKET MILK. Ss 
Milk custard.—Thinking that possibly the rennet added to 
the milk might produce some deleterious action on the bacteria, 
a similar medium has been tried in which the casein is precipi- 
tated by the use of an egg. Milk is mixed with an egg, both 
the white and the yolk, and the whole is thoroughly boiled. 
The result of the boiling is a curdling of the milk, and after 
curdling the whole material is strained through cheesecloth, 
and the whey sterilized in the autoclav as above described. 
The further treatment is identical with the above, the only dif- 
ference in the preparation of these two media being in the use 
of the egg rather than the rennet for the precipitation of the 
casein. Practically, the material is much more difficult to make 
than the whey gelatin. 
Peptone culture media.—The third culture medium is the 
ordinary beef peptone gelatin such as is prepared for most bac- 
teriological work and described elsewhere. ‘This material is 
made with 1334 per cent. of gelatin and placed in test tubes, 8 
cubic centimeters exactly being placed in each tube. The rea- 
son for the high per cent. of gelatin and the exactness of the 
8 cubic centimeters in the tubes will appear below. 
METHOD OF USING THE ABOVE MEDIA. 
The method of using any of the culture media above de- 
scribed with the litmus solution is as follows: Several tubes 
of any of the litmus culture media above prepared are melted, 
and into each by means of a sterilized pipette is placed 2 cubic 
centimeters of the litmus solution. The whole is mixed together 
by gentle agitation, giving 10 cubic centimeters of solution 
with a deep blue color. The mixture has a percentage of gela- 
tin of about 11 per cent., this being the percentage which we 
have found most satisfactory for our purpose. ‘The reason for 
using exactly 8 cubic centimeters of a 15 per cent. solution is that 
the mixture may be brought to 12 percent. gelatin. Itis evident 
also that if the litmus should prove to be weak, so that more 
than 2 cubic centimeters of the solution are required to give 
the proper depth of blue, a smaller amount of gelatin solution 
must be placed in each tube and a higher per cent. of gelatin. 
A more convenient way of adjusting this is, however, to use 
