144 BACTERIOIvOGlCAL EXAMINATION OF MILK. 



tare of milk, character of original container (tank, can, bottle), etc., 

 should be written opposite duplicate numbers in a blank book or pocket 

 card catalogue, or this information may be written on small tags and 

 tied or wired to the corresponding test tube or bottle. 



Teinperature. The temperature should be taken immediately after 

 taking the sample for anal3'sis, while the milk is still thoroughly mixed. 



If it is desired to take the temperature of ' ' certified milk, ' ' this should 

 be done when the sample is taken, but from another bottle. 



A floating thermometer, graduated to the Fahrenheit scale, -is most 

 convenient, and the temperature should be expressed to the nearest 

 degree. It is necessary to standardize the thermometer for at least ten 

 degrees on each side of the legal temperature limit. A quickly regis- 

 tering thermometer should be left at least one minute in the milk and 

 read as soon as removed. A small piece of clean absorbent cotton ma}' 

 be used to wipe the adhering milk from the thermometer that the scale 

 may be easilj^ seen. 



Representative samples. The collector should always select his own 

 sample, and care should be taken to secure a sample which is truly rep- 

 resentative of the milk to be examined. 



One of several methods of mixing the milk may be used, comparison 

 having shown the results to be practicall}' the same (9). 



1. Pouring the milk into a sterile receptacle and back. 



2. Shaking the milk thoroughly with receptacle turned upside down. 

 (This may be done where the can or bottle is tightl}' stoppered or capped 

 and is not so full as to prevent thorough agitation.) 



3. In open tanks in stores it is allowable to stir thoroughlj- with the 

 long-handled dipper generally found in use. 



4. Where the test tube collecting case is used, thorotighly reliable 

 results are secured by first shaking the can or bottle ; and, second, stir- 

 ring with the large pipette before taking the sample, care being taken to 

 close the upper end of the pipette with the finger so that no milk enters 

 until after the mixing, or the pipette may be emptied after stirring before 

 the sample is taken. 



5. For certified milk samples it is recommended that, on arrival at 

 the laborator)', the bottle be opened with aseptic precautions and the 

 milk thoroughlj' mixed by pouring back and forth between the original 

 bottle and a sterile bottle. Another method is to mix as thoroughly as 

 possible Ijy agitation for five minutes, then burn through the paste-board 

 stopper with a hot iron and remove the desired amount of milk with a 

 sterile pipette (13). 



The interval between collection and analysis. Generally speaking the 

 shorter the time between the collection and examination of milk samples 

 the more accurate will be the results. For routine work the attempt 

 should be made to plate within foiir hours of the time of collection. 



Too much stress cannot be laid on keeping the samples properly iced 



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