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 magnification shall not be considered in the 

 count. 



69. Records of Bacteriologic 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. 



4 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. 



