314 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
precautions after the milk has been thoroughly mixed by vigor- 
ously reversing and shaking the container twenty-five times. 
64. Two plates at least shall be made for each sample of 
milk, and there shall also be made a control of each lot of 
medium and apparatus used at each testing. The plates shall 
be grown at 37° C, for forty-eight hours. 
65. In making the plates there shall be used agaragar media 
containing 1.5 per cent. agar and giving a reaction of 1.0 to 
phenolphthalein. 
[The method recommended by a committee of the American 
Public Health Association for the making of the medium is to 
be followed (see page 262), modified, however, as to the agar 
content and reaction to conform to the requirements specified 
in section 65. | 
66. Samples of milk for plating shall be diluted in the pro- 
portion of 1 part of milk to 99 parts of sterile water; shake 
25 times and plate 1 c.c. of the solution. 
[The recommendations of the committee of the American 
Public Health Association in regard to plating are to be fol- 
lowed: (see page 265).] 
67. Determination of Taste and Odor of Milk.—After the 
plates have been prepared and placed in the incubator, the 
taste and odor of the milk shall be determined after warming 
the milk to 100° F.4 
68. Counts.—The total number of colonies on each plate 
should be counted, and the results expressed, in multiples of the 
dilution factor. Colonies too small to be’seen with the naked 
eye or with slight magnifitation shall not be considered in the 
count. 
69. Records of Bacieriologic Tests.—The results of all bac- 
terial tests shall be kept on file by the secretary of each commis- 
sion, copies of which should be made available annually for the 
use of the American Association of Medical Milk Commissions. 
* Should it be deemed desirable and necessary to conduct 
tests for sediment, the presence of special bacteria, or the num- 
ber of leucocytes, the methods adopted by the committee of the 
American Public Health Association should be followed. 
