CULTIVATION OF THE BACILLUS 89 



also give an account of experiments carried out to 

 test the relative value of the human, bovine, and 

 avian types of tubercle bacilli. On pp. 267-268 they 

 state : 



'* Twort and Ingram found that the best growth 

 v^as obtained on Dorset's egg medium to which 

 timothy bacilli (bacillus phlei) had been added, but 

 apparently tubercle bacilli of the human type were 

 in this respect only slightly inferior. On the other 

 hand, they obtained little or no growth on media 

 with which the avian type of tubercle bacillus had 

 been incorporated, and the results were entirely 

 negative when bovine tubercle bacilli were em- 

 plo3^ed. 



" Our results are not at all concordant with these. 

 In comparative experiments we have generally 

 found that tubercle bacilli of the avian type gave 

 the best results, and that human bacilli were 

 slightly superior to the bacillus phlei. The word 

 'generally' has been used in the preceding sen- 

 tence because absolutely uniform results are not 

 obtainable with different lots of media prepared 

 in the same way, and it has therefore occasionally 

 happened that no difference could be observed 

 between parallel cultures according as the medium 

 contained the one or the other kind of acid-fast 

 bacillus. The most striking difference of opinion, 

 however, has arisen in connection with the use ot 

 tubercle bacilli of the bovine type. As stated above, 

 Twort and Ingram found this type of organism 

 useless for the purpose in view, and they appear to 

 have thought that in this fact they had discovered 

 evidence contrary to the view that the human and 

 bovine types are only slightly different varieties of 

 one and the same organism. We have found that 



