86 JOHNE^S DISEASE 



" For these reasons, and quite independently of 

 Holth's attempts in the same direction, we en- 

 deavoured to obtain some other medium for the 

 cultivation of the bacilli. 



" As it appeared to be probable that the essential 

 substance present in the mixture of eggy tubercle 

 bacilli, and glycerine was something extracted 

 from these bacilli by the glycerine, it was resolved 

 to endeavour to obtain a strong glycerine extract 

 of tubercle bacilli, which when added to agar or 

 other transparent medium might render that suit- 

 able for the growth of Johne's bacilli. 



" The dead bodies of tubercle bacilli cultivated 

 on the surface of 5 per cent, glycerine broth were 

 therefore extracted with hot glycerine, and after 

 removal of the bacilli the glycerine extract was 

 added to various media, which were then inoculated 

 with Johne's bacilli. This immediately yielded 

 positive results, and enabled us to obtain good 

 growths on media that were at once transparent 

 and free from tubercle bacilli. 



" For purposes of extraction various strengths 

 of glycerine were employed, but a better extract 

 appeared to be obtained with diluted glycerine 

 than with the pure substance." 



In our paper (Royal Society, B. 84, 1912, communi- 

 cated November 7, 191 1), to which the authors in their 

 paper have frequently referred, we do not suggest that 

 media must be made of egg and tubercle bacilli ; various 

 modifications are discussed, including those mentioned 

 by M'Fadyean, Sheather, and Edwards. On p. 525 we 

 stated : 



" Experiments showed that ^ to i per cent, of 

 the dried tubercle bacillus was the most suitable 



