CHAPTEE XXVII. 

 GROUP IV. 



Infectious diseases which usually are chronic, 

 but may run acute courses. They are characterized 

 by marked local tissue changes, which exert a lim- 

 iting influence on the processes, and include the 

 infectious granulomata, excepting syphilis. Infec- 

 tion produces little or no immunity. In some in- 

 stances the prolonged immunization of animals in- 

 duces increased resistance to infection (tuberculo- 

 sis) ; in other instances this has not been deter- 

 mined, or is difficult of determination because of 

 the non-susceptibility of the animals used to 

 the corresponding infections. The serums of im- 

 munized animals, in so far as this subject has been 

 investigated, show little or no protective or cura- 

 tive power. 



I. TUBERCULOSIS. 



Klemke, in 1843, but more particularly Ville- 

 min, in 1865, demonstrated the infectiousness of 

 tuberculosis by animal experiments, and these re- 

 sults were substantiated later by such investigators 

 as Klebs, Chauveau, Baumgarten and Cohnheim. 

 Baumgarten first saw the tubercle bacillus in sec- 

 tions of tuberculous material from which the tis- 

 sue cells had been dissolved by potassium hydroxid, 

 and at almost the same time Koch succeeded in 

 demonstrating its presence in all tuberculous 

 lesions by a special staining method. He eventu- 

 ally obtained the organism in pure cultures with 



