DEVELOPMENT OF CITY MILK SUPPLY PROBLEMS 41 
infect the milk,*t under ordinary conditions the contamina- 
tion of the milk arises almost exclusively from the utensils 
in which it is handled.2?, Among the utensils the milking 
machine,** 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 a3 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 ec. c.** to as high as 2,000,000 per c. ¢.** 
A very practical difficuity 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, 
31K, G. Hastings and C. Hoffman, Bacterial Content 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 Cows, 
Tech. Bul. 27, N. Y. Agr. Exp. Sta., 1913. 
2M. J. Prucha, H. M. Weeter and W. H. Chambers, Germ Content of 
Milk as Influenced by the Utensils, Bulletin 204, Ill. Agr. Exp. Sta., 1918. 
%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-drawn 
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. 8S. Public Health Reports, 29, 
pp. 1218-1221, 1914. 
33 Limit for potable milk set by ordinance at St. Louis, Mo. 
