254 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



centers have become encapsulated and frequently calcified, and that 

 there has been no formation of new tuberculous centers. 



Dr. Vallee believes that we must recognize that, in spite of the 

 enormous benefits realized on all sides, none of the proposed methods 

 of vaccination has yet furnished definite results. He states : 



1. Nevertheless, the inoculation of cattle by any method with 

 virulent human tubercle bacilli confers an appreciable resistance 

 against various methods of experimental infection and also against 

 natural contagion. 



2. The resistance conferred is directly proportional to the quan- 

 tity and virulence of the bacilli injected, but however great their 

 value, the immunity conferred by them does not persist longer than 

 12 to 18 months. 



3. The introduction of living bacilli as a vaccine contaminates 

 the entire organism. This peculiarity necessitates a special guard 

 over the animals immunized, should they be sent to slaughter during 

 the six months which follow the last vaccination. 



4. Whatever the mode chosen for introducing the vaccine, the 

 resistance conferred is insufficient to assure the complete resorption of 

 the bacilli inoculated for prolonging immunity. 



5. The resistance to infection by the digestive tube of the animal 

 vaccinated by that method is incomparably superior to that acquired 

 by animals by the intravenous method, because it permits the organ- 

 ism to obtain complete resorption of the virulent material inoculated. 

 Considering the frequency of infection through the digestive canal in 

 cattle, the application of vaccinating material through the mouth ap- 

 pears preferable to every other method. 



6. Vaccination by the digestive method can not be made entirely 

 free from danger of infection if one uses virulent bacilli of the bovine 

 type. The use of bacilli of the human type of slight virulence is, 

 therefore, preferable, as these furnish results comparatively equal to 

 those of the bovine type. 



7. Vaccination by way of the mouth is not easily obtained ex- 

 cept upon very young subjects. 



8. Vaccination by way of the mouth does not place the animals 

 entirely beyond danger of infection with tuberculosis. It permits 

 them to resist for more than a year contact with cattle which present 

 open lesions of tuberculosis and, following this, present no lesions be- 

 yond insignificant tubercular nodules in the various glands. On this 

 account it merits systematic study and further practical application. 



9. The resistance conferred by subcutaneous methods is inferior 

 to that obtained by way of the circulation. 



10. Vaccination by the use of killed bacilli has given results in- 

 ferior to those obtained with living and virulent organisms. 



11. No definite conclusion can yet be actually formulated in re- 

 gard to the various methods of immunization under discussion, but 

 their systematic application will permit a determination of their real 

 practical value. 



The method of immunization proposed by Arloing does not ex- 

 actly resemble any of the other systems which are at present in use. 



