3 o CLEAN MILK 



discharge) contaminate the surroundings, dust, utensils, water, 

 fodder, etc., and so may find their way into milk, as they do 

 into well animals. While it has generally been thought that the 

 tuberculosis germs in milk are commonly derived from the udder 

 of the diseased cow it now seems probable that the contamination of 

 milk with manure of tuberculous cows is the most frequent source 

 of the germ. Mohler has found the germs of tuberculosis in the 

 manure of over 41 per cent, of cows of healthy appearance which 

 showed no evidence of tuberculosis save by the tuberculin test. 

 The tuberculosis germs present in the manure are, however, chiefly 

 derived, not from disease of the bowel, but from the blood or dis- 

 charge coughed up from the lungs and then swallowed by the animal. 



The results of the examinations of some 1,287 samples of 

 milk, chiefly by intraperitoneal injection into guinea pigs and rab- 

 bits, by some 18 or 20 experimenters in different European cities, 

 show that 9% of milk contains active germs of tuberculosis. 

 Anderson has shown that in Washington, D. C, approximately 

 1 1 % of the dairies supply milk containing virulent tubercle bacilli. 



The percentage of cows affected with tuberculosis varies widely 

 in different herds and localities. Thus large herds are more apt 

 to be tuberculous and 80 to 90% of the animals may have tuber- 

 culosis. In smaller herds and in those living chiefly outdoors 

 the percentage may vary from zero to 50% affected with the 

 disease. Of 24,685 cows tuberculin-tested in Massachusetts, 50% 

 were found to be tuberculous. The latest statistics (1908) concern- 

 ing the prevalence of tuberculosis among cattle in the United States 

 ar-e those of Melvin based on approximately '54 million cattle 

 slaughtered and inspected for food, and 400,000 (mostly dairy 

 cattle) tested with tuberculin. 



He estimated that ten per cent, of milch cows and one per cent 

 of other cattle have tuberculosis. The use of tuberculin is the only 

 positive test. 



Just how common, and how important, therefore, is tubercu- 



