76 JOHNE'S DISEASE 



medium. This slowly increased, spreading over the 

 surface of the medium and becoming more heaped 

 up. The colour was a dull white, slightly tinged with 

 yellow. These broth cultures were used for preparing 

 our first series of diagnostic vaccines. 



We now proceeded to test our strains of Johne's 

 bacillus on media in which the dead tubercle bacillus 

 was replaced by various other micro-organisms. We 

 soon found that some strains of human tubercle bacilli 

 were more suitable than others; and, further, that if 

 the human tubercle bacillus was replaced by the bovine 

 type, no growth of Johne's bacillus took place, and that 

 this was so even when subcultured from strains that 

 had been growing outside the animal body for a year. 

 Several strains of tubercle bacilli isolated from cats 

 were also tested, but gave negative results. The cat 

 strains were distinctly bovine in character, and, as was 

 the case with the other tubercle bacilli, they were 

 grown on Dorset's egg medium. (A discussion of 

 these results and some details of further experiments 

 with the bovine strains are given later.) 



In view of Johne andjFrothingham's original sugges- 

 tion that the bacillus of pseudo-tuberculous enteritis 

 was either an avian tubercle bacillus or some variety 

 of it, and the support this view received from the re- 

 actions to avian tuberculin obtained by Bang in animals 

 suffering from Johne's disease (vtde Chapter VII.), the 

 avian tubercle bacillus naturally suggested itself for 

 incorporation in media. Two strains, therefore, were 

 tested ; one was obtained from Krai, and the other 

 isolated by ourselves from a natural case of tubercu- 

 losis in a hen. The bacilli were grown on large tubes 

 of Dorset's egg medium, and when the growth had 

 reached a maximum it was killed, scraped off, dried, 

 and made up into medium as already described for the 



