No. 7. DEPARTMENT OF AGRICULTURE. 607 



of common salt. We inject this solution into the circulation; that 

 is, the injection is made into the jugular vein, and at varying inter- 

 vals the injection is repeated. One of the purposes of our experi- 

 ment is to ascertain just what doses is necessary and just what 

 intervals between doses should be employed and just how many 

 doses gives the best results. So you can see that it is necessary 

 to try different experiments on a considerable number of animals 

 for the purpose of gaining information on these points. Another 

 point that it has been necessary to gain information upon is with 

 relation to the duration of the immunity that is produced by this 

 system. Our first experiments showed that by repeating the vacci- 

 nation several times it was then possible to inoculate the animal with 

 a virulent culture that caused death in a short time in unvaccinated 

 animals, and that the vaccinated animal will resist the inoculatioii 

 with the virulent culture. When such vaccinated animals were 

 killed some weeks after the inoculation with the virulent germs, 

 it was not possible to find any trace of infection, while in the unvacci- 

 nated animals that were inoculated at the same time with the quan- 

 tity of the same culture, very distinct lesions of tuberculosis were 

 found. Indeed, some of our unprotected animals died within a short 

 time as a result of this inoculation. 



THE CATTLE IN THE EXPERIMENT. 



We have under experiment now about one hundred cattle. These 

 are kept on a farm that has been provided for this purpose by the 

 State Livestock Sanitary Board in Delaware county. The cattle 

 that are on that farm are of three sorts. There are the vaccinated 

 cattle, the cattle that have been vaccinated in different ways, with 

 different intervals between vaccinations and with different numbers 

 of vaccinations. That is one class of animals. Then there are the 

 unvaccinated cattle which are kept there for the purpose of com- 

 parison. Then there is a considerable number of tubercular cows, 

 cows in an advanced stage of tuberculosis. Now, vaccinated cattle 

 and unvaccinated cattle are in constant daily contact with the tuber- 

 cular cows, the idea being to continue this exposure for a consider- 

 able time, for several years indeed, and from time to time to kill 

 the vaccinated and the unvaccinated cattle with the view to ascer- 

 tain whether the unvaccinated cattle are infected and the vaccinated 

 cattle are protected, and what system of vaccination gives most sat- 

 isfactory results, so that we may know the system that we may 

 depend upon in actual practice. 



We have already proved that by a sufficient number of vaccina- 

 tions a thoroughly practicable degree of immunity can be afforded; 

 but, of course,, the .value of the process will depend largely upon 

 the economy with which it can be applied, and so without going 

 below the safety point, we want to know just how few vaccinations 

 will give the result that is desired. 



FAVORABLE RESULTIS. \ 



Eecently, during the last month, we have killed a number of these 

 experimental cattle. In the last lot destroyed there were six that 

 had been vaccinated and three that were not vaccinated. Of these 



