Methods of Extermination. 597 



complete extermination of the disease. By removing the necessity of maintaining 

 two separate herds it is less objected to by the owner but the results achieved are 

 correspondingly unsatisfactory. J<>om 1900-01 to 1903-04 among 15,000 adult cattle 

 1,071 cases of open tuberculosis were diagnosed, during whi^jh time the percentage 

 was reduced to 1.3% but since that time and up to 1908-09 it has been reduced 

 only to 1.2% (Mueller, Ostertag). In the herds of the East Prussian Herd Book 

 Association for Mottled Eed Cattle the percentage has been reduced from 3.2 to 

 1.24 in the course of six years; in Pommerania, in the course of five years, from 

 2.93 to 0.39%; in Brandenburg, in the course of five years, from 2.28 to 0.7% 

 (in the. first 20 herds, including 2,131 animals, which were subjected to this method, 

 the percentage was reduced from 4.1 to 0.23%). In Schleswig-Holstein, in four 

 years the reduction was from 2.8 to 1.47% and in the Province of Saxony, in four 

 years, from 3.6 to 1.18% (Ostertag). These percentages, of course, all refer to 

 open tuberculosis. Whether or not the total number of all cases of tuberculosis 

 were correspondingly diminished or whether there may have been an actual increase 

 is not recorded! At all events the figures furnished show that the results obtained 

 bear no comparison whatever with those obtained by the Bang method. 



In infected herds of swine the disease may be successfully stamped 

 out by eliminating the affected animals upon the basis of the outcome 

 of the tuberculin test, subsequent thorough disinfection of quarters 

 and the observation of the necessary precautions to prevent the rein- 

 troduction of the disease (Thiro). 



Immunization. Basing Ms observation upon the specific 

 identity but varying pathogenic action of human and bovine 

 tubercle bacilli, v. Behring, in 1901, declared that by treating 

 cattle with the less virulent human tubercle bacilli they would 

 be protected against the more actively virulent bovine tubercle 

 bacilli and thus also against natural infection with tuberculosis. 

 On the basis of this assertion several methods of immunization 

 for cattle have been recommended and actually carried out in 

 practice. More or less satisfactory results however were ob- 

 tained in such eases only where hygienic and prophylactic ^ 

 measures, effective in themselves, were instituted at the same 

 time. 



Double Immunization with Human Tubercle Bacilli (Immunization 

 with bovo-vaccine ; Behring 's method). The immunizing material con- 

 sists of nearly full-virulent human tubercle bacilli, dried in a vacuum 

 and injected into the blood circulation of calves. The first tests con- 

 ducted after these treatments showed that two intravenous injections 

 of bovo-vaccine, or of any fresh culture of the human type of tubercle 

 bacillus into cattle resulted in a considerable and immediate increase 

 in their power of resistance to artificial infection. Calves thus treated 

 would, as a rule, resist successfully four months later intravenous 

 injections of virulent bovine bacilli in doses that proved invariably 

 fatal in untreated calves. Further experiments, however, showed that 

 resistance thus artificially increased was of short duration, suffering 

 considerable reduction at the end of one year and disappearing entirely 

 six months later. On the other hand, the results of the practical 

 application of the method in herds showed that it had no noticeable 

 effect on the improvement of the health of infected herds. Since im- 

 munization produces no harmful effect upon previously healthy calves, 

 it might" he possible to prolong their immunity indefinitely by annual 

 vaccinations. The objection to this plan, aside from its attendant trouble 

 and expense, lies in the fact that the bacilli introduced by the act 

 of vaccination remain alive and active in the bodies of the animals 



