PATHOGENIC BACTERIA. 295 



culosis in cows, see page 148. Supposing that some cura- 

 tive principle exists in the bodies of the tubercle bacilli 

 themselves which could not be procured from cultures de- 

 prived of their bacilli by nitration through porcelain, Koch 

 has recently proposed a new form of tuberculin called 

 " tuberculin R," which consists of an extract made from 

 dried and pulverized living tubercle bacilli. The value of 

 this new tuberculin as a remedy is at least doubtful, and 

 physicians are disposed to regard it with a great deal of 

 caution. 



Immunity from tuberculosis has been attained experimentally to a 

 certain degree. In very old cultures the virulence of tubercle bacilli 

 sometimes becomes greatly diminished. Animals which survive injec- 

 tions of such bacilli may afterwards withstand large doses of virulent 

 bacilli. 1 



Acid-proof bacilli resembling tubercle bacilli have been alluded to 

 a number of times (pages 149, 154, and 288). A number of such bacilli 

 have been cultivated, such as those of butter and grass. Injected into 

 animals they may produce nodules more or less like tubercles. In these 

 nodules they sometimes assume forms resembling the fungus of actino- 

 mycosis. The tubercle bacillus rarely shows similar forms. All the 

 bacilli of this class, including the tubercle bacillus, sometimes show 

 branching. It is probable that the bacilli of this group are related to 

 the fungus of actinomycosis. 2 Similar organisms have been found in 

 fishes, in whom they produce nodules resembling tubercles; it is quite 

 possible that the latter organisms are tubercle bacilli, which have been 

 modified by an altered environment. Another acid-proof bacillus has 

 been found which is pathogenic to rats, producing lesions of the skin 

 with nodules ; the disease appears in wild rats in certain localities. 



Tuberculosis of Birds. Fowls, ducks and other birds sometimes 

 suffer from tuberculosis due to a bacillus closely resembling the tubercle 

 bacillus of mammals. It has similar staining properties. It sometimes 

 grows in long, branching forms. It differs somewhat from the tubercle 

 bacillus of mammals in its cultural properties. The liver is the organ 

 most often affected. Guinea-pigs are much less susceptible to it than to 



'Truder.ti, Neiv York Medical Journal, July 18, 1903. Salmon, Phila- 

 delphia Medical Journal, June 13, 1903. 



2 Abbott and Gildersleeve, University Pennsylvania Medical Bulletin, 

 June, 1902. 



