172 MILK AND THE PUBLIC HEALTH chap. 



Collection of Samples. — Care in coUectiou is necessary to 

 obtain samples which are really representative of the milk 

 to be examined. Ordinary samples of mixed milk may be 

 collected at the byres or in course of transit or delivery. The 

 cream and the sediment are the richest in bacteria, so that it 

 is necessary to well mix the milk before a sample is withdrawn. 

 If a sample representing all the mixed milk of the cows at 

 the byre is required, it will be necessary for the collector to 

 remove a definite quantity {e.g. half a gallon) from each churn 

 and mix all the fractions in a clean empty churn or other 

 vessel, and take the sample from this. 



In the collection of samples from individual cows care 

 must be taken to avoid outside contamination. The cows' 

 udders and teats must be washed carefully, and the milker 

 must wash and disinfect his hands. The milk is milked 

 direct into the bottle, the stopper being held by a second 

 person by its free end to avoid contamination, and inserted 

 immediately after the sample has been collected. The bottle 

 should not have too narrow a mouth. In some cases it may 

 be sufficient to collect a mixed sample from the four quarters, 

 and then care should be taken to as nearly as possible obtain 

 equal quantities of milk from each teat. In other cases it is 

 necessary to collect a separate sample from each quarter. In 

 general the fore milk should be rejected and middle milk 

 sampled. In rare instances it may be necessary to collect 

 fore, middle, and end milk samples from one special quarter 

 or all of them. 



In the examination of sterilised milk or ordinary bottled 

 milk an unopened bottle must be selected and used, or two or 

 more bottles may be obtained and a representative sample 

 made up from these. 



The milk should be collected in sterile bottles with 

 accurately fitting glass stoppers. For the ordinary examina- 

 tion of mixed milk a sample of about a pint is a convenient 

 amount to obtain, but for most purposes a much smaller 

 quantity is sufficient. The larger amount obviates some of 

 the possible errors in sampling from irregular distribution of 

 the bacteria. 



For samples from individual cows 2 oz. of milk is a suffi- 

 cient quantity. The glass-stoppered bottles are sterilised in their 



