Tuberculosis. 513 



But the bacillus from the lungs is subject to variations of this 

 kind. Among seven specimens of human sputum, cultivated by 

 Theobald Smith, six had a fair average vitality, while the seventh 

 failed to perpetuate itself on dog serum. ^ 



It should be strongly emphasized in this connection that the 

 failure of extension and generalization of the sputum germ when 

 transferred to cattle does not distinguish it from the tubercle 

 bacillus as conveyed from ox to ox. Everyone at all experienced 

 with the tuberculin test well knows that in most herds the majority 

 of the tuberculous animals show no generalization, but only a local' 

 ized tuberculosis. There is reason to believe that even recoveries 

 take place after slight infection, and it is certain that many tuber- 

 culous cattle continue for years in what appears to be good general 

 health. Unless in particularly susceptible subjects or under 

 specially poor hygienic conditions, or unless in case of reinfec- 

 tion, the average bacillus of bovine origin habitually fails to pro- 

 duce in other cattle a rapid extension and generalization. 



3. Inter changeability of Bacillus of Man and Bird. Of all 

 known forms of tubercle bacillus that of birds is the most distant 

 from that of man or ox, and yet the beautiful experiments of 

 Nocard ^ serve to establish their essential identity. Taking the 

 bacillus of human sputum, which would not infect the fowl, he 

 enclosed it in collodion capsules, which confined the bacilli while 

 allowing transudation of the animal fluids, and left these in the 

 abdomen of the chicken for not less than four months. He 

 repeated this three times in succession with the product of the 

 original sputum germ, and obtained a bacillus which was ac- 

 tively pathogenic for the chicken, though it had been harmless 

 after the sojourn of four and eight months respectively. 



This may explain the reported cases in which a flock of poultry 

 have developed tuberculosis a few months after they were placed 

 in the hands of a consumptive caretaker. That such transmission 

 does not always occur is not surprising, considering that trans- 

 mission between man and man is infrequent in comparison with 

 the number of exposures. So in cattle the majority of exposed 

 animals usually escape, although in such a case there can be no 

 plausible explanation on the ground of a difference of germ. We 



1 Journal of Experimental Medicine, 1898, No. iii. 

 * Annales de I'Institut Pasteur, September, 1898. 

 33 



