i 7 4 MILK AND THE PUBLIC HEALTH CHAP. 



size the writer uses is made to just hold four 2 oz. bottles 

 and their tins, but larger bottles are more convenient for milk 

 samples. 



The growth of bacteria in milk kept at ice temperature, or 

 only slightly above C., has been considered in Chapter IV. 

 While, as explained in that chapter, some bacterial changes 

 take place at these low temperatures, there is no material 

 alteration or error of judgment involved in examining samples 

 kept iced for not more than 12 to 20 hours. 



Particulars to record with the Samples. These must be 

 carefully recorded, and should include : 



(a) Date and time of sampling. 



(5) Identification particulars as to farm or person from 

 whom the milk is obtained. 



(c) If mixed milk or from individual cows. 



(d) If mixed milk, whether collected from byre, in transit, 

 in shop, etc., or as delivered. 



(e) If collected at the byre, the number of cows the milk of 

 which it is a sample should be given, and whether the milk 

 has been strained or not, and if so the strainer used. 



(/) If from individual cows, particulars of the quarter or 

 quarters from which obtained, and if fore, middle, or end milk. 



It is useful to take and record the temperature of the milk. 



Dilution of the Sample. In the bacteriological examina- 

 tion of milk the proper dilution of the sample is of the utmost 

 importance if accuracy is to be obtained. It is equally 

 important that the milk should be thoroughly well shaken 

 before dilution, and that the dilutions should be well mixed. 



Eosenau and McCoy 1 have shown that the number of 

 bacteria in milk, as determined by plating, is affected by the 

 extent to which the milk sample and dilutions have been 

 shaken. This is also shown by the influence of milk separators 

 on the bacterial count. 



Plating whole milk without dilution is always unreliable, 

 even if the milk contains but few bacteria, since the bacteria 

 are not properly separated, while the addition of the milk causes 

 turbidity and so obscures the bacterial colonies. 



The following is the most convenient method of dilution. 

 A large number of glass-stoppered bottles of about 120 c.c. 



1 Journ. Med. Research, 1908, xviii. p. 165. 



