History, Occurrence. 501 



of the disease among animals, though less far reaching in their effects, 

 have also been gratifying. 



The results which were for a time expected from the curative value 

 of tuberculin (Koch, 1890) were realized to a slight extent only. On 

 the other hand tuberculin has proven itself a valuable diagnostic agent 

 and has been used with particular success among domestic animals. The 

 diagnostic properties of tuberculin and the recognization of the condi- 

 tions which produce infection constitute the basis of Bang's system for 

 the extermination of tuberculosis. By means of this system the eradi- 

 cation of the disease can be accomplished without serious economic loss 

 even in badly infected herds. On the other hand, the advantages ex- 

 pected from protective inoculation of cattle by means of human tubercle 

 bacilli (Behring, 1902) have by no means been realized in the same 

 degree, and the problem of employing this agent in the fight against 

 tuberculosis remains for the future to solve. 



Among the more recent discoveries which deserve special mention 

 are Pirquet's local "allergic" tuberculin reactions and Much's non-acid- 

 fast form of tubercle bacillus. 



Occurrence. The prevalence of tuberculosis, especially 

 among cattle and swine, stands in intimate relation to the de- 

 velopment of intensive agriculture. Among cattle its spread 

 is favored to a great extent by our modern soiling system, 

 forced maturity of young animals and increased traffic in live 

 stock. Thus tuberculosis is practically unknown on the ex- 

 tensive prairies of North America, in Central Africa and on 

 many islands (Iceland, Sicily). It is almost unknown among 

 the cattle of the steppes of Eastern Europe, while it is par- 

 ticularly prevalent in the central and western countries of 

 Europe, especially in the neighborhood of large cities where 

 it is increasing in prevalence. Large dairy establishments near 

 cities suffer comparatively greater losses than the smaller herds 

 of farmers in mountainous regions. Young animals are less 

 frequently affected than older stock. Among swine the disease 

 has gained a foothold through the practice of feeding the prod- 

 ucts of creameries and skimmed milk to young swine. Among 

 other domestic animals, with the exception of fowls, the disease 

 is much less prevalent, although no species is entirely free from 

 its ravages. 



The importance of tuberculosis to the cattle industry lies 

 in the fact that the average age of usefulness of the young 

 animals has decreased in direct proportion to the increased 

 prevalence of tuberculosis, and to the fact that the losses from 

 the elimination of indifferent and poor milk producers are con- 

 tinually increasing. The raising of young animals is attended 

 with greater difficulties and expense ; the volume of milk pro- 

 duced by infected herds is decreased, and the emaciation of 

 affected animals reduces their food value. Moreover the large 

 number of carcasses of diseased animals which are condemned 

 for food purposes causes annually a considerable economic loss 

 to the national wealth. 



Our knowledge of the prevalence of the disease has been 

 gained on the one hand from statistics furnished by public 



