248 TUBERCULOSIS 



tubercles. Tuberculosis can also be easily produced in susceptible 

 animals by making them inhale the bacilli. 



Varieties of Tuberculosis. 1 . Human and Bovine Tuberculosis. 

 Up till recent years it was generally accepted that all 

 mammalian tuberculosis was due to the same organism, and 

 in particular that tuberculosis could be transmitted from the 

 ox to the human subject. The matter became 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 

 necessary to take any measures against it. Previously to this, 

 Theobald Smith had pointed out differences between mammalian 

 and bovine tubercle bacilli, the most striking 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. Koch's conclusions were based 

 chiefly on the result of his inoculations of 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. 



Since the time of Koch's communication an enormous amount 

 of work has been done on this subject, and Commissions of 

 inquiry have been appointed in various countries. We may 

 summarise the chief facts which have been established. 

 Practically all observers are agreed that there are two chief 

 types of tubercle bacilli which differ both in their cultural 

 characters and in their virulence a bovine type and a human 

 type. The bacilli of the bovine type when cultivated are shorter 

 and thicker and more regular in size ; whilst their growtETon 

 various culture media is scantier than that of the human type. 

 From the latter character the British Royal Commission have 

 applied the term dysgonic to the bovine and eugonic to the 

 human type. As already stated there is also a great difference 

 in virulence towards the lower animals, the bacillus from the ox 

 having a much higher virulence. This organism when injected 

 in suitable quantities into the ox produces a local tubercular 

 lesion, which is usually followed by a generalised and fatal 

 tuberculosis ; whereas injection of human tubercle bacilli pro- 

 duces no more than a local lesion, which undergoes retrogression. 

 (In certain experiments, e.g. those of Delepine, Hamilton and 



