METHODS OF EXAMINING MILK 261 



milk may be mixed by inverting the bottle several times. 

 If the milk is in a vessel which is open and which can- 

 not therefore be inverted, it may be stirred with the 

 pipette which is used to transfer the sample to the sample 

 bottle. The pipette should, of course, be sterile and 

 should not be used to take another sample until it has 

 again been sterilized. A sterile tube with straight sides 

 should be used for taking a sample from a can. An 

 aluminum tube % inch in diameter and 21 inches long 

 is most convenient. If the tube is held vertically, with 

 the opening at the top unobstructed, and is inserted into 

 the milk slowly until the lower end reaches the bottom of 

 the can, it will contain a column of milk which will be 

 representative of all the milk in the can. If the finger 

 is then placed firmly upon the top of the tube, the column 

 of milk can be withdrawn and transferred to a sterile 

 sample bottle, which should be large enough to hold the 

 entire contents of the tube, all of which must be emptied 

 into the bottle. The tube must be washed and sterilized 

 before being used to collect a sample from another con- 

 tainer. If the temperature of the milk is to be taken, a 

 separate sample should be used for this purpose and then 

 discarded. Glass-stoppered bottles or those provided 

 with cork-lined screw caps are the most satisfactory. The 

 bottle containing the sample should be properly labelled 

 and immediately placed in a carrying case containing 

 cracked ice so that the milk will be promptly cooled to 

 near the freezing point. The sample bottles should be 

 transferred to the laboratory as soon as possible and the 

 milk plated at once. If the plates are not prepared within 

 four hours after the collection of the samples the elapsed 

 time should be noted in the report. If the samples are 



