DEVELOPMENT OF CITY MILK SUPPLY PROBLEMS 41 



infect the milk/' 1 under ordinary conditions the contamina- 

 tion of the milk arises almost exclusively from the utensils 

 in which it is handled. 32 Among the utensils the milking 

 machine/ 13 where it is used, the shipping can, and the cooling 

 and bottling machinery at the milk plant are ordinarily the 

 principal sources of this contamination. 



The problem of a suitable test for the keeping quality of 

 milk is not as simple as might at first appear. 



Since the keeping quality of milk depends upon germ life, 

 the number of germs present has been suggested as the logical 

 measure of keeping quality, and this idea has been accepted 

 by a considerable number of municipalities. However, there 

 seems to be no basis for an agreement as to the maximum 

 number of bacteria to be used as a standard of proper keeping 

 quality. Actual municipal standards vary from as low as 

 50,000 per c, c. 34 to as high as 2,000,000 per c. c. 33 



A very practical difficulty with bacterial standards is the 

 extreme variations which occur in determining the germ 

 content of milk even under the most favorable conditions. 

 This was most strikingly illustrated in a comparative test 

 made under the direction of Dr. H. W. Conn and conducted 

 cooperatively in four laboratories in New York City. These 

 studies showed that occasionally plate determinations made 

 from milk approximately sour indicated a lower germ content 

 than other plate determinations made from certified milk, 



31 E. G. Hastings and C. Hoffman, Bacterial Conient of the Milk of Indi- 

 vidual Animals, Research Bulletin 6, Wis. Agr. Exp. Sta., 1909. 



H. A. Harding and J. K. Wilson, A Study of the Udder Flora of Coivs, 

 Teeh. Bui 27, N. Y. Agr. Exp. Sta., 1913. 



32 M. J. Prucha, H. M. Weeter and W. H. Chambers, Germ Content of 

 Milk as Influenced by the Utensils, Bulletin 204, 111. Agr. Exp. Sta., 1918. 



x-i F. C. Harrison, Machine-drawn Milk Versus Hand-Drawn Milk in 

 Cent. F. Bak., II. Abt. 5, 183-189, 1899. 



E. G. Hastings and C. Hoffman, Bacterial Control of Machine-draivn 

 and Hand-drawn Milk in Annual Report, Wis. Agr. Exp. Sta., 24 (1907), 

 214-222. See also Cent. f. Bak. II. Abt. 22, 222-231, 1908. 



H. A. Harding, J. K. Wilson and G. A. Smith, Milking Machines: Effect 

 of Method of Handling on the Germ Content of Milk. Bulletin 317, N. Y. 

 Agr. Exp. Sta., 1909. 



34 Bacteriological Standards for Milk, U. S. Public Health Reports, 29, 

 PP. 1218-1221, 1914. 



35 Limit for potable milk set by ordinance at St. Louis, Mo. 



