BACILLUS OF TUBERCULOSIS. 265 



methylene-blue with caustic potash. More recently 

 Ehrlich devised a method of staining which proved 

 to be better, viz., the use of a solution of an aniline 

 color fuchsin or methyl-violet in a saturated aqueous 

 solution of aniline oil and decolorization of other bac- 

 teria with a solution of a mineral acid, to be followed 

 by a contrast stain, such as methylene-blue. (Plate 

 I., Figs. 1 and 2.) Various modifications of Ehrlich's 

 method are now commonly used. The carbol-fuchsin 

 solution of Ziehl is largely employed ; it has the advan- 

 tage of acting quickly and keeping well. The tubercle 

 bacilli can be demonstrated also by Gram's method of 

 staining, but this is not recommended for general use. 



Biological Characters. The bacillus tuberculosis is a 

 parasitic, aerobic, non-motile bacillus, and .grows only 

 at a temperature of about 37 C. It has been assumed 

 that this bacillus is capable of forming spores. The 

 refractile spaces, however, are not found to possess the 

 regular shape and brilliancy of ordinary spores, nor have 

 they any greater resisting power to heat, desiccation, 

 etc., than the homogeneous bacilli. Exposure to 60 C. 

 in water destroys them in fifteen minutes. The bacilli 

 have, however, a somewhat greater resisting power than 

 most other pathogenic bacteria, since frequently the 

 bacilli resist desiccation at the ordinary temperatures 

 for months; many bacilli die, however, soon after dry- 

 ing. Portions of the lung from a tuberculous cow, dried 

 and pulverized, produced tuberculosis in guinea-pigs at 

 the end of 102 days (Cad&ic and Malet). They retain 

 their vitality for a considerable time in putrefying ma- 

 terial. Cold has no effect upon them. When dry the 

 more resistant organisms stand dry heat at 100 C. for 

 hours; but when moist, as in milk, they are more quickly 



