526 Messrs. Twort and Ingram. Isolating and [Nov. 7, 



J ohne's bacillus and incubated at 39° to 40° C, with the following results : — 

 Growth took place on the medium containing the human type and on the two 

 containing both types, but no growth took place on that containing only the 

 bovine type. This experiment proves fairly conclusively that the unsuit- 

 ability of the bovine type of bacillus is not due to the presence of any toxic 

 body in its substance, otherwise no growth would have taken place on the 

 media containing the mixture of the two bacilli. We may note, however, 

 that we have not tested many strains of the bovine bacillus, and it is possible 

 that Johne's bacillus will grow on some bovine strains, or on those strains 

 which have been described as occupying an intermediate position between the 

 typical human and typical bovine bacilli ; but we have no evidence that 

 this is so. 



Whatever this difference between the two types of bacilli may be due to, 

 it does not in our opinion necessarily represent an important biological 

 difference ; it is probably physiological in nature, and may be due to the 

 presence or absence of some reserve food material existing or otherwise 

 outside the strictly vital portion of the bacillus, or it may be due to some fat, 

 wax, or other covering material preventing this substance from being utilised 

 by Johne's bacillus. In the light of some recent experiments the latter 

 possibility seems improbable, as we have been unable to extract any 

 substance suitable for the growth of Johne's bacillus. These experiments are 

 being continued. 



While in this paper we cannot enter into the controversy concerning the 

 relationship between the human and bovine types of tubercle bacilli, yet, 

 incidentally, we venture to remark that, in spite of all that has been written 

 in this country, we are not yet convinced that the human and bovine types 

 are only slightly different varieties of one and the same micro-organism. In 

 this connection the difference between the two bacilli described above may be 

 worthy of note and further investigation. 



The failure to obtain any growth of Johne's bacillus on media containing 

 tubercle bacilli isolated from bovines and cats led us to seek for other acid- 

 fast bacilli which might act as substitutes for the tubercle bacillus of man, 

 and two bacilli at once suggested themselves. As we have already remarked, 

 0. Bang has shown that avian tuberculin may cause some reaction with 

 pseudo-tuberculous enteritis of bovines, and the possibility of the avian 

 tubercle bacillus and Johne's bacillus being closely allied is at once obvious. 



Accordingly we prepared several batches of medium containing the avian 

 tubercle bacillus in place of the human type. On this medium our strains of 

 Johne's bacillus usually grew, but only slightly, and the medium proved to 

 be quite unsuitable for practical purposes. 



