CERTIFIED MILK 219 



62. Interval between milking and plating. — The examinations shall 

 be made as soon after collection of the samples as possible, and in no 

 case shall the interval between milking and plating the samples be 

 longer than 40 hours. 



63. Plating. — The packages shall be opened with aseptic precau- 

 tions after the milk has been thoroughly mixed by vigorously reversing 

 and shaking the container 25 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 48 

 hours. 



65. In making the plates there shall be used agar-agar media con- 

 taining 1.5 per cent agar and giving a reaction of 1.0 to phenolphthalein. 



66. Samples of milk for plating shall be diluted in the proportion 

 of 1 part of milk to 99 parts of sterile water ; shake 25 times and plate 

 1 c.c. of the dilution. 



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. 1 



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 he seen with the naked eye or with slight mag- 

 nification shall not be considered in the count. 



69. Records of bacteriologic tests. — The results of all bacterial tests 

 shall be kept on file by the secretary of each commission, copies of 

 which should be made available annually for the use of the American 

 Association of Medical Milk Commissions. 



Chemical Standards and Methods 



The methods that must be followed in carrying out the chemical 

 investigations essential to the protection of certified milk are so com- 

 plicated that in order to keep the fees of the chemist at a reasonable 

 figure, there must be eliminated from the examination those proce- 

 dures which, whilst they might be helpful and interesting, are in no 

 sense necessary. 



For this reason the determination of the water, the total solids, 

 and the milk-sugar is not required as a part of the routine examination. 



70. The chemical analyses shall be made by a competent chemist 

 designated by the medical milk commission. 



1 Should it be deemed desirable and necessary to conduct tests for 

 sediment, the presence of special bacteria, or the number of leucocytes, 

 the methods adopted by the committee of the American Public Health 

 Association should be followed. 



