VACCINES: DIAGNOSTIC AND CURATIVE 109 



cient is given. On the other hand, it must be remem- 

 bered that vaccines prepared from almost any acid-fast 

 bacillus will produce a reaction in such conditions as 

 tuberculosis, leprosy, and Johne's disease, provided 

 that a sufficiently large dose is given ; but with such a 

 dose animals suffering from other diseases, and normal 

 animals are very liable to react, and from this it follows 

 that any reaction obtained in the test animal is worth- 

 less or even misleading. 



To obtain a specific and reliable diagnostic vaccine, 

 it should be prepared from the same species of bacillus 

 that causes the particular disease, in which case it is 

 necessary to give only a relatively small dose to pro- 

 duce a reaction, in fact, a dose sufficiently small to 

 avoid a definite reaction in animals suffering from 

 allied diseases or by normal animals. Other factors 

 remaining constant, it may be said in general that the 

 closer the relationship between the specific variety of 

 bacillus causing the disease and the bacillus from 

 which the vaccine is prepared, the more reliable and 

 specific the test becomes. 



In the case of Johne's disease the absence of a pure 

 culture of Johne's bacillus led several workers to 

 investigate vaccines prepared from allied acid-fast 

 bacilli. O. Bang, in 1907, tested cattle suffering from 

 pseudo-tuberculous enteritis with a vaccine made from 

 B. phlei, and the present writers have since tested a 

 strain of B. phlei in the same way, both on naturally 

 infected and on artificially inoculated animals. 



In 1907-08 O. Bang tested cattle suffering from 

 Johne's disease with a tuberculin prepared from 

 tubercle bacilli isolated from birds. The vaccine used 

 was prepared from a four months' old glycerine-broth 

 culture. The filtrate obtamed from this culture was 

 evaporated to one-tenth the original volume, and one 



