172 JOHNE'S DISEASE 



of bacilli, and the bacilli increase in number up to the 

 eighth or ninth day, long after the temperature has 

 fallen. However, it must be remembered that at this 

 stage, although the bacilli are numerous, they are 

 surrounded by a dense wall of small round cells, and 

 it is significant that the appearance of these cells 

 coincides with the fall of the temperature. A detailed 

 discussion of these facts is hardly within the scope 

 of this book ; it only remains to be borne in mind 

 that such a condition of affairs does not exist when 

 Johne's bacillus is inoculated. The ultimate death of 

 the animal appears to be due to the pathological condi- 

 tion of the kidney. 



If now we consider Johne's bacillus, we find a condi- 

 tion similar to that obtained when using killed B. phlei. 

 The absence of a rise of temperature is probably due 

 either to the rapid death of the micro-organism, or to 

 the lack of formation of any free toxin ; we are inclined 

 to favour the latter hypothesis in view of the similar 

 condition found in naturally infected bovines. The 

 survival of rabbits is undoubtedly due to the main- 

 tenance of the normal condition of the kidneys, through 

 which the bacilli are slowly filtered, and owing to the 

 death of the bacilli, or to their inability to grow in this 

 situation, the kidneys remain more or less in an 

 uninjured state. 



Thus it appears that although Johne's bacillus is 

 pathogenic for certain ruminants, it is, nevertheless, 

 one of the least toxic of the acid-fast group of micro- 

 organisms, and we have seen that the majority of 

 animals possess a natural resistance against the 

 bacillus. We believe, too, from the distribution of 

 the bacillus in naturally affected animals, and from the 

 experiments on the cultivation of the bacillus, that the 

 question of a special food-supply may play an impor- 



