252 E VOL UTION AND DISEASE. 



In man tubercle affects any organ and tissue of the 

 body, and is due to the entrance and multiplication 

 in the body of a micro-organism, the tubercle bacillus, 

 identified by the genius of Koch. Until the discovery 

 of this bacillus in tubercular lesions it was customary to 

 apply the term tubercle to almost any disease which was 

 characterized by the formation of nodules in the tissues, 

 thus the term came to have a generic rather than a 

 specific signification. Now that we have a pathological 

 criterion of tubercle, the term tuberculosis has a definite 

 meaning, and certain affections formerly included are 

 now known to be due to other causes, and numerous af- 

 fections formerly excluded now help to swell the list of 

 troubles due to this omnipresent micro-organism. 

 Among other mammals the disease has a peculiar 

 distribution ; it is very common among cattle under the 

 name of grape disease, or its German equivalent, Perl- 

 sucht. Monkeys living in confinement in this country 

 are occasionally attacked by it, but not so frequently as 

 was formerly supposed. Among grain-eating birds the 

 disease is a perfect scourge ; the flesh-eating birds are 

 not so liable to contract it, and are probably not in- 

 frequently attacked in consequence of devouring tuber- 

 cular grain-eating birds. In quadrumana and man the 

 disease runs a similar course, whilst in cattle the lesions 

 are so different, that it would be difficult to believe that 

 it is in any way related to the tuberculosis of Primates, 

 were it not for the existence of identical micro- 

 organisms, and this again applies equally to birds in 

 whom the lesions differ from those in man and cattle. 

 It is also extremely difficult to understand the immunity 

 of horses, tuberculosis being rare among Equida. 



