DIFFERENTIAL DIAGNOSIS. 357 



solid media are whitish, soft, and moist, becoming yel- 

 lowish and slimy with age ; it is somewhat more resist- 

 ant to drying and high temperatures than the bacillus 

 of mammalian tuberculosis ; the results of its patho- 

 genic activities are almost always chronic, are rarely 

 located in the lungs or intestines, but are especially fre- 

 quent in the liver and spleen ; the lesions are conspic- 

 uously rich in bacilli, do not show the central necrotic 

 area that characterizes the mammalian tubercle ; the 

 disease is transmissible from the hen to the embryo 

 chick ; the only susceptible mammal is the rabbit ; the 

 guinea-pig and dog are naturally immune ; it has the 

 same micro-chemical staining-reactions as mammalian 

 bacillus tuberculosis ; it has never been certainly de- 

 tected in human tuberculosis. 



Some are inclined to regard this organism as but a 

 variety of the genuine bacillus tuberculosis, and it is not 

 unreasonable to believe that the sojourn of that organ- 

 ism in the body of a refractory animal, whose normal 

 temperature is so high as that of the fowl, when not fatal 

 to the organism, might result in striking modifications 

 of certain of its biological functions. In fact, Nocard ' 

 has shown that if the genuine bacillus tuberculosis from 

 man be left in the peritoneal cavitj' of chickens (by the 

 collodion-sac method of Metschnikoff, Roux, and Sal- 

 lembini, which see) for from five to eighth months, they 

 will, by the end of this time, have become so modified 

 in their biological peculiarities as to simulate very 

 closely the bacillus of fowl tuberculosis. 



Theobald Smith ^ has called attention to certain very 



1 Nocard : Annates de I'lnstitut Pasteur, 1898, p. 561. 

 ^ Smith : Transactions of the Association of American Physicians, 

 1896, vol. xi. p. 75. 



