1^4 PRACTICAL DAIRY BACTERIOLOGY 



of supply, 10,000 to 50,000 being frequently found; but even in 

 these, places many samples of milk show much larger numbers. 1 



With such wide variations it clearly becomes difficult to de- 

 termine upon any standard of numbers. At present, only in a 

 few places has the attempt been made to establish such a stand- 

 ard. Boston has tried to enforce a standard of 500,000 per c.c., 

 while it has been doubted whether New York could .reach a 

 standard of 1,000,000. Smaller standards than either are aimed 

 at by some smaller cities, and for special grades of milk 30,000, 

 or even 10,000, are sometimes demanded. Of course, it is not 

 to be assumed that the milk that comes to New York is twice 

 as dirty as that which reaches Boston, and hence it is evident 

 at the outset that the number of bacteria alone is not a satis- 

 factory means of determining the cleanliness of the milk. 



The method of determining the number of bacteria in milk 

 is fairly simple. Special collecting cases are provided, con- 

 taining vials capable of being closed and cooled with ice. 

 (Fig. 58.) These are filled with samples of milk to be tested, 

 from the cars, delivering wagons or elsewhere. In collecting 

 the samples it is necessary to stir thoroughly the contents of 

 the can or jar which is to be sampled, and, of course, to de- 

 termine and record with accuracy its source. Care in collecting 

 the sample is of the utmost importance, for the milk at the bot- 

 tom and the top of a can may be quite different. It is also 

 customary to test the temperature of the milk at the same time 

 and make a careful record. The samples thus collected are to 

 be packed in ice and carried immediately to the laboratory. 

 In the laboratory they should be immediately tested by ordinary 

 methods, agar culture media being used in most cases at a dilu- 

 tion of 1,000 (see page 273), the plate being incubated at a tem- 



1 Jordan. Analyses of Chicago Market Milk. Chicago, 1904. 

 Park and Bebb. N. Y. University Bui. 1., No. 2, 1901. 

 Harrison. Trans, of Canadian Inst., vii., p. 467, 1902-3. 

 Bergy. Univ. of Pa. Med. Bui., 1904. 



