398 BACTERIA IN INFECTIOUS DISEASES. 



ease, in which the essential etiological agent is the 

 bacillus discovered by Koch. The possibility that 

 the special pathogenic power of this bacillus is an 

 acquired rather than an essential physiological 

 character, depending upon the fact that it has 

 been bred for many successive generations in a 

 tuberculous soil, and that it is in truth a pathogenic 

 variety of a common and widely distributed species, 

 seems to be worthy of further consideration. 



Dr. Watson Cheyne of London, a very compe- 

 tent, witness in a case of this kind, has repeated 

 Koch's experiments, and fully confirms him in all 

 essential particulars. 



This author paid a visit to Toussaint and to 

 Koch for the purpose of making himself familiar 

 with their methods. Upon his return to England, 

 a series of experiments was made, with the results 

 reported below. 



The experiments were made under the most 

 favorable hygienic conditions, and all possible pre- 

 cautions were taken as regards disinfection of 

 instruments and the complete isolation of the ani- 

 mals used. Twenty-five animals, inoculated with 

 non-tubercular material in various ways, failed to 

 become tuberculous. In six of these, setons were 

 introduced subcutaneously ; in ten, vaccine lymph 

 was employed ; in three, pyoemic pus was injected ; 

 and in six, various materials were introduced into 

 the abdominal cavity (cork, tubercle hardened in 

 alcohol, worsted thread). Cheyne believes that 

 in similar experiments 'made by other observers, in 

 which a positive result has been reported, the 



