Methods of Extermination. 595 



The free herd should be retested with tuberculin every year so 

 that animals that were infected and failed to react at a previous test, 

 or that have become infected since that time, may be removed and 

 added to the quarantine herd. Newly acquired animals should under 

 no circumstances be added to the free herd unless they have been found 

 free from evidences of tuberculosis by physical examination and tuber- 

 culin test made immediately before. 



Males used for breeding purposes should, if at all possible, be 

 free, not only from every suspicion of tuberculosis, but should other- 

 wise be in perfect health. If unavoidable, a reacting male may be 

 used but such animals should at least be free from clinical evidence of 

 disease. Such an animal must, of course, be kept under constant super- 

 vision during the act of coitus and never be permitted to run with 

 the free herd. 



By this method the nonreaeting or free portion of the herd will 

 constantly increase in numbers while the reacting herd may be cor- 

 respondingly reduced in size without interfering with the amount of 

 business transacted with the products. Eventually the reactors can 

 be entirely eliminated and a herd free from tuberculosis remain in 

 place of the original infected herd. This can be accomplished with 

 comparatively light expense, and with proper attention and occasional 

 retests with tuberculin the herd may then be kept free permanently 

 from tuberculosis. 



The extermination of tuberculosis after the method of Bang has found its 

 widest application in Denmark, Sweden and Norway where government support 

 is liberally extended and favorable results have been quite general. As a result 

 of the personally conducted campaign of Bang, in Denmark, the average percentage 

 of reacting animals in 1893 (40%) has been reduced in 1908, to 8.5%. Among 

 calves the average percentage in 1893 (15.5%) has been reduced to 10.6 in 1898. 

 Up to the year 1904, 66 badly infected herds comprising 1,045 reactors and 780 

 healthy animals have been entirely freed from disease, the 66 herds consisting at 

 that time of 1,896 healthy animals. In Norway, according to Malm, the percentage 

 of reactions has been reduced from 8.4% in 1896 to 4.9% in 1903, and the proportion 

 of inspected herds that were found infected was reduced from 26.1% to 13.6%. 

 In Sweden, where, in the beginning of the campaign of extermination (in 1897-98) 

 11,089 out of 33,000 animals reacted to the tuberculin test, i. e., 33.6%, reports for 

 the year 1904 showed that among 34,996 cattle tested only 1,664, i. e., 4.7% reacted. 

 During this interval 214 herds comprising 8,205 animals were freed from the disease 

 (Eegn6r.) — ^In Finland reactions reached 25% in 1894 while they were reduced to 

 10.1%. by 1900 (Hojer). In Hungary there exists now a number of large dairies 

 in which the percentages of reactors have been reduced in the course of a few years 

 to 2 or 3 per cent without any reduction in the size of the herds. Thus on the 

 Mezoehegyeser government estate the first tuberculin test which was conducted in 

 the spring of 1898 in a herd of 329 cows revealed 44.8% of reactors while 26.6% 

 of the total number tested (647) reacted. In the fall of the year 1903 a test of 503 

 cows on the same estate gave only 2.8% of reactors and "a test of all of the cattle 

 on the estate (1,132) gave 1.8% of reactors. During this period of five years the 

 herd on this estate was increased 75% in numbers by addition of its own offspring, 

 while the prevalence of tuberculosis was reduced 88% (Hutyra). 



The favorable results of feeding calves with sterilized milk are illustrated by 

 the following: In Sarv4r 93.8% of the calves thus reared gave no febrile reaction 

 to Behring's protective inoculation while only 42.1% of the calves reared under 

 usual conditions responded similarly. (Behring's protective inoculation, when applied 

 io tuberculous animals, gives a reaction similar to that of tuberculin.) On several 

 German estates, where similar experiments were conducted, the proportions were 

 74.2% and 48.1% respectively. 



Modification of Bang's Method. In only slightly infected herds 

 where the question of expense is not the first consideration the quickest 

 results may be obtained by slaughtering all reacting animals at once. 

 In this way the necessity of maintaining two herds, one healthy and 



