XT"MEKICAI, DETERMINATION OF BACTERIA. 143 



Since at best oiilj- approximate results can be reached in the numerical 

 determination of bacteria in milk, and since from the varyintj methods 

 in use at present counts from different workers are usually incomparable, 

 those methods which have given best results as a whole should be united 

 upon and adopted by all, that a bacterial count on a sample of milk may 

 mean the same if made in any standard laboratory. 



Collection of Samples. 



Quantity of milk required for analysis. The minimum quantity of 

 niilk necessary for making an ordinary bacteriological examination is ten 

 cubic centimeters. When making examinations for certified milk, if 

 pos.sible a pint or quart bottle should betaken and brought to the laljor- 

 atorj' unopened. 



Collecting apparatus. In collecting milk samples for bacteriological 

 examination it is essential that the sample be taken and kept in such a 

 manner as to prevent either anj- addition of bacteria from without or 

 multiplication of the bacteria originally present (9. Bottles, tubes, 

 pipettes, etc., used in the collection of samples, besides being washed, 

 shall be sterilized with dry heat for an hour at or about 160° C, or to the 

 charring point of cotton. 



In the selection of "certified milk " samples it is recommended wher- 

 ever pos.sible that an unopened liottle be taken, placed in a suitably iced 

 case and brought at once to the laboratory. 



Samples of "market milk" may be collected as are water samples, 

 in sterile, wide-mouthed, glass-stoppered four-ounce bottles ; the case in 

 which they are carried being well iced (10). The principal diHicult\ 

 encountered in this method is in transferring the sample from the origi- 

 nal container to the bottle, and the various string and wire devices l>y 

 means of which the bottle is inunersed in the original container are 

 objectionable both on account of the labor of preparing such an outfit 

 and also on account of the coating of milk left on the outside of the 

 bottle when the .sample has been taken. 



An apparatus de.signed for the use of thirty-two test tubes as containers 

 (11) is reconmiended as .superior to one designed for bottles. 



It has been proven that with samples kept properly iced in this par- 

 ticular form of case there is no increase of bacterial content even for 

 twenty-four hours, but rather a slight decrease (7), the counts varying 

 hardly more than might be expected in duplicate plates. It is recom- 

 mended, however, that examination of the samples be proceeded with as 

 quickly as possible after the collections are made. 



Identification of samples. When bottles are used identification num- 

 bers should be etched on both bottle and stopper. Test tubes should be 

 labeled or etched (12) ami numbered. 



A complete record of the samples taken, giving ilate, time, place, 

 name of part^■ from which .sample is taken, name of collector, tempera- 



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