232 MARKET DAIRYING 
cle bacilli are frequently found in milk is abundantly 
shown by actual statistics. 
Some years ago an investigation was made of the 
milk supply of the city of Washington by the Hygienic 
Laboratory, Public Health and Marine Hospital Service, 
Washington, D. C. This investigation disclosed the 
fact that approximately 11% of the milk of 100 or more 
dairies investigated contained tubercle bacilli. Out of 
1287 samples of milk collected in fourteen European 
cities, including London, Liverpool, Paris, St. Peters- 
burg, Berlin and Copenhagen, 144, or 11.2%, contained 
tubercle bacilli. 
Bacterial Counts. One of the common aids em- 
ployed in determining the purity of milk is to count the 
number of bacteria contained in it. In general there is 
a fair relation between the number of bacteria and the 
purity of the milk, and when the bacteria count is sup- 
plemented with an inspection of the conditions under 
which the milk is produced and handled it has consider- 
able value. On the other hand, we should not forget 
that a bacterial count alone is likely to lead to very 
erroneous conclusions regarding the wholesomeness of 
milk. To illustrate, let us compare two milks produced 
under identical conditions as to cleanliness. If one of 
the milks has been promptly cooled to 45° F. and kept at 
this temperature it may contain only 5000 bacteria per 
c. c. while the other sample, if poorly cooled, may contain 
1,000,000 per c. c. The higher temperature has given 
the bacteria in the latter sample an opportunity for rapid 
development while the temperature (45° F.) of the 
former sample has checked the growth of the bacteria 
contained in it. If the milks were produced under clean- 
ly conditions, the increase in the number of bacteria in 
