102 JOHNE^S DISEASE 



obtained slight growth on a medium that contained 

 0*2 per cent, of glycerose. The strain of Johne's 

 bacillus had been grown on timothy-grass bacillus- 

 egg medium for about twelve months, but still gave 

 no indication of growth on ordinary Dorset's egg 

 medium. 



Although from the experiments it appears that not 

 one of the acids enumerated above is identical with 

 the essential substance, yet the results obtained with 

 glycerinic, tartronic, and gluconic acids are interesting, 

 and it is possible that the acid constituting the essen- 

 tial substance is allied to the acids mentioned. More 

 recently we have tested other organic acids, including 

 various tartaric, oxalic, and phosphoric acids. We 

 have also tested acids that contain other elements — 

 chlorine, nitrogen, or sulphur — in combination ; but 

 all the results were negative. 



Although we have been unable to discover an 

 efficient substitute for the essential substance, our 

 experiments, considered as a whole, certainly suggest 

 that it is some organic acid. However, whatever its 

 nature may be, it will probably be difficult to obtain 

 sufficient material to determine its constitutional for- 

 mula, although in the future it may be found possible 

 to discover the nature of the constituent elements, and 

 the structure of the essential organic radicle in the 

 molecule. 



The relationship of Johne's bacillus to the tubercle 

 bacilli and other acid-fast bacilli, and the possibility 

 that the essential substance may influence the patho- 

 genicity of Johne's bacillus, are discussed more fully at 

 the end of Chapter IX. 



In the light of future research, some of the theories 

 we have put forward may prove to be wrong ; but we 

 have thought it advisable to give them, not only that 



