VACCINES : DIAGNOSTIC AND CURATIVE 133 



case when testing advanced cases of tuberculosis with 

 tuberculin. As some of our cases of advanced Johne's 

 disease were suffering from concomitant tuberculosis, 

 the question arises as to whether the presence of the 

 latter disease did not possibly mask the reaction in 

 a few cases. 



As in most biological tests, specificity can only be 

 obtained by an exact system of dosage, and it is for 

 this reason that the use of avian tuberculin in Johne's 

 disease has been proved to be practically worthless. 

 We have seen that in Johne's disease undoubted 

 reactions were obtained by Bang, Miessner, etc., by 

 the use of an avian tuberculin, but the reactions were 

 more often negative than positive; and there is no 

 doubt that to attain a larger percentage of positive 

 results the dose of this vaccine would have to be such 

 that it would be beyond the limits of reliability, and 

 tubercular or even sound animals might give a re- 

 action. 



It is probable that in the future modified vaccines 

 will be prepared from cultures of Johne's bacillus, and 

 that other methods of inoculation will be resorted to. 

 In the case of tuberculins many different methods of 

 preparation and administration have been published, 

 and we have seen that Bang, Malm, Male, and, more 

 recently, M'Fadyean, Sheather, and Edwards, have 

 tested some of these modifications on animals suffering 

 from pseudo-tuberculous enteritis. It appears to us, 

 however, unlikely that there will be much improve- 

 ment on the subcutaneous inoculation of a vaccine 

 prepared from an ordinary glycerine-broth culture of 

 Johne's bacillus, although the ophthalmic test with 

 the same vaccine may be useful under certain 

 circumstances. 



At the present day nearly all cattle have to undergo 



