HUMAN AND BOVINE TUBERCULOSIS. 251 



be transmitted from the ox to the human subject. The matter 

 has become one of special interest owing to Koch's address 

 at the Tuberculosis Congress in 1901, in which he stated his 

 conclusion that human and bovine tuberculosis are practically 

 distinct, and that if a susceptibility of the human subject to the 

 latter really exists, infection is of very rare occurrence, so 

 rare that it is not advisable to take any measures against it. 

 Previously to this, Theobald Smith had pointed out differences 

 between mammalian and bovine tubercle bacilli, the most im- 

 portant being that the latter possess a much higher virulence 

 to the guinea-pig, rabbit, and other animals, and in particular that 

 human tubercle bacilli, on inoculation into oxen, produce either 

 no disease or only local lesions without any dissemination. He 

 also found that the bovine bacilli on cultivation grow less vigor- 

 ously for a time, and tend to be shorter and straighter than the 

 human bacilli. Koch's conclusions were based chiefly on the 

 result of his inoculations in the bovine species with human 

 tubercle bacilli, the result being confirmatory of Smith's, and, 

 secondly, on the supposition that infection of the human subject 

 through the intestine is of very rare occurrence. With regard 

 to this opinion, we must disagree with Koch, as in our experi- 

 ence there is considerable evidence that in young subjects the 

 intestinal canal is a comparatively common path of entrance ; 

 and, moreover, the presence of pulmonary lesions does not prove 

 that infection has occurred by inhalation, as in many cases the 

 pulmonary lesions are secondary to those in the bronchial 

 glands, whilst the infection of the cervical or mesenteric glands 

 is of still older standing. There may also be infection of the 

 mesenteric glands without actual lesions in the intestine. That 

 the ox is little susceptible to human bacilli may be accepted, but 

 it does not follow that the converse is true, namely, that the 

 human subject cannot be infected from the bovine species, 

 seeing that bovine tubercle bacilli have been found to have 

 a greater virulence for all animals tested than bacilli from 

 the human subject. Moreover, there are cases, notably those 

 recorded by Ravenel, in which direct inoculation of the human 

 subject with bovine tubercle has occurred. Even if the human 

 subject is little susceptible to bovine tuberculosis, it is quite 

 likely, in view of the large proportion of young subjects ex- 

 posed to infection, that the number of cases of tuberculosis pro- 



