74 PRINCIPLES AND PRACTICE OF MILK HYGIENE 
percent. In Philadelphia, in 1908, Campbell ? examined 
130 samples of raw milk and found tubercle bacilli in 
13.8 per cent.; twelve samples of milk sold as “ pasteur- 
ized ” were also examined by him and one sample, or 8.3 
per cent., contained virulent tubercle bacilli. Hess * 
found tubercle bacilli in 16 per cent. of the samples he 
examined in New York in 1909, and of 144 samples ex- 
amined by Tonney in Chicago in 1910 10.5 per cent. were 
infected with tubercle bacilli. In Germany, from 16.5 
to 27.1 per cent. of the samples of market milk examined 
in various cities contained tubercle bacilli; in England, 
10 to 25 per cent.; in Paris, 20 per cent., and in Copen- 
hagen, 4 per cent.* Another evidence of the frequency 
of tubercle bacilli in milk is the general virulence of sep- 
arator milk from creameries. This milk has been found 
to be such a great factor in the dissemination of tubercu- 
losis among calves and hogs that several states, among 
them Pennsylvania, have passed laws requiring such milk 
to be pasteurized before it is removed from the creamery 
to be fed to cattle or swine. 
There are no statistics which show definitely the ex- 
tent to which tuberculosis exists among dairy cattle in 
the United States. The disease is found in less than 1 
per cent. of the cattle slaughtered for meat under Federal 
inspection, but the greater proportion of these are beef 
cattle and many of them are of young age, a period when 
tuberculosis is not as frequently found as in later life. 
The proportion of dairy cows affected with tuberculosis 
is not known. The per cent. of infected animals varies 
2 26th Annual Report, B. A. I., pp. 175-177. 
3 The Incidence of Tubercle Bacilli in New York City Milk, 
Jour. Am. Med. Assoc., No. 13, Vol. 52. 
* Rievel, Milchkunde, pp. 99-100. 
