294 MANUAL OF BACTERIOLOGY. 



Immunity from tuberculosis has been attained experimentally to a certain 

 degree. In very old cultures the virulence of tubercle bacilli sometimes be- 

 comes greatly diminished. Animals which survive injections of such bacilli 

 may afterwards virithstand large doses of virulent bacilH.* 



Acid-proof bacilli resembling tubercle bacilli have been alluded to a num- 

 ber of times (pages 138, 143 and 287). 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 actinomycosis. 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.f 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 Uver is the organ most often affected. Guinea- 

 pigs are much less susceptible to it than to mammalian tuberculosis. Rabbits 

 are somewhat susceptible, though less so than to mammalian tuberculosis. 



Pseudotuberculosis. — Guinea-pigs and other rodents sometimes present 

 lesions macroscopically very similar to those of tuberculosis, in which, how- 

 ever, the tubercle bacilli cannot be found. These affections appear not to be 

 tuberculosis at all, and their nature is tiot well understood. Several organisms 

 have been found in them, all of which are entirely unHke the tubercle bacillus. 



Bacillus leprae (bacillus of leprosy). — ^A slim bacillus about 

 4 /Jt in length. It is probably not motile. It is uncertain whether 

 or not it forms spores. It stains by the Gram and the Weigert 

 fibrin method, and it is also colored by the methods used for 

 staining the tubercle bacillus. It takes the dye, however, 

 more readily than the tubercle bacillus. In stained prepara- 

 tions it appears very similar to the tubercle bacillus, and re- 



* Trudeau. New York MedicalJournal. July 18, 1903. Salmon. Phila- 

 delphia Medical Journal. June 13, 1903. 



t Abbott and Gildersleeve. University oj Pennsylvania Medical Bulletin. 

 June, 1902 



