314 A MANUAL OF BACTERIOLOGY 



induces a progressive disease with large caseating masses. 1 

 These distinctions were regarded as being due to variations 

 in the bacilli as a result of growing upon a different soil 

 and not to any fundamental difference between the two 

 strains of bacilli. In 1901, however, Koch stated 2 that 

 young cattle and swine cannot be infected with human 

 tuberculous material, and he therefore concluded that 

 human and mammalian tubercle bacilli are essentially 

 different. As a result of his experiments he made the 

 statement that " though the important question whether 

 man is susceptible to bovine tuberculosis at all is not yet 

 absolutely decided, if such a susceptibility really exists, 

 the infection of human beings is but a very rare occurrence." 

 This view met with considerable opposition, and a 

 second Royal Commission was appointed to investigate 

 the question, and the following summarises the results 

 obtained up to the present, from which it will be gathered 

 that while there is no justification for assuming that man 

 is infected from human sources alone, infection from 

 human sources is probably vastly more frequent than 

 from any other. Thirty different viruses isolated from 

 cases of tuberculosis occurring spontaneously in bovines 

 have been studied, and the results of introducing them 

 into a number of different animals by feeding and inocula- 

 tion are recorded. In calves, inoculation usually results 

 in generalised progressive tuberculosis, but the effect is 

 somewhat dependent on the dose, i.e. the number of bacilli, 

 administered. Thus whereas 50 mgrm. of culture always 

 induced a fatal generalised progressive tuberculosis, in 

 two instances much smaller doses 0'01-0'02 mgrm. 

 produced only limited retrogressive tuberculosis. Feeding, 

 on the other hand, usually produced lesions limited to 



1 The bacill derived from tuberculosis of the sheep, pig, and horse 

 (pulmonary lesions) are also of the bovine type. 



2 See Brit. Med. Journ., 1901, vol. ii, p. 189. 



