MILK-BORNE INFECTIONS 445 



and human tuberculosis were caused by the same organism, but 

 Theobald Smith called attention to distinct differences between the 

 human and bovine bacilli. Koch in 1901 went so far as to inti- 

 mate that the disease in man and cattle was caused by totally dif- 

 ferent organisms, and that no precautions were necessary to protect 

 human life against infection with the bovine bacillus. This state- 

 ment has so effectively stimulated scientific investigation that an 

 enormous amount of work -has accumulated to indicate that, 

 although infections of man with the bovine tubercle bacillus are 

 fewer than infections with the human variety, bovine infections 

 and deaths resulting therefrom are frequent enough to seriously 

 engage the attention and activity of sanitarians. 



Tuberculosis among cattle has both an economic and a sani- 

 tary aspect. 



The loss of live stock from tuberculosis is difficult to measure. 

 Cattle suffering from the disease lose in value whether they are 

 beef producers or milkers. A single animal suffering from tuber- 

 culosis may infect a whole herd. The loss of live stock from 

 tuberculosis is enormous. Probably at least 10 per cent, of dairy 

 cows are tubercular, and loss among hogs is no less. Moore found 

 that among 421 herds in New York State, 302 contained cattle 

 reacting to tuberculin. The total number of cows was 9633, and 

 3432 of these reacted. Russell and Hoffmann, in Wisconsin, found 

 363 herds infected among 1562, and 263 herds were infected 

 through purchase. The financial loss from tuberculosis among 

 cattle and hogs is difficult to estimate, of course. Not only do 

 some cattle and hogs die, but others lose flesh and the quantity 

 of milk is materially reduced. It is certain that the loss amounts 

 to millions of dollars annually. According to Melvin's estimate, 

 the total loss among farm animals in the United States is at least 

 $14,000,000 annually. 



The most important methods of dissemination of the disease 

 are these : 



1. Contact with infectious material in stables, railway cars, in 

 pastures, etc. 



2. Introduction of diseased animals into sound herds, either 

 by purchase or by contact at public exhibitions. 



3. Feeding calves on unpasteurized milk, skimmed milk, or 

 whey from infected animals. 



1. Tuberculosis is an insidious disease of unknown and prob- 

 ably variable incubation period. Cows may have the appearance 

 of perfect health; they may eat well and show no symptoms of the 

 disease and still be afflicted with it. In such cases the lesions are 

 usually small. Progress of the disease is more or less rapid, 

 according to the resistance of the animal. Sanitary stables, 



