TUBERCULOSIS. 307 



upon acid potato mixed with glycerin, also found that 

 upon such compounds its virulence was constantly lost. 

 According to French writers, the virulence of the bacillus 

 is not diminished when it grows upon potato. It has 

 also been said that the continued cultivation of the 

 tubercle bacillus upon culture-media lessens its parasitic 

 nature, so that in the course of time it can be induced to 

 grow feebly upon the ordinary agar-agar, and that pro- 

 longed cultivation destroys its virulence. - 



In a letter recently received from Ravenel, I learn 

 that &{Xsx jive years' continuous cultivation upon artificial 



Fig. 68. — Bacillus tuberculosis : adhesive cover-glass preparation from a fourteen- 

 day-old blood-serum culture; x 100 (Frankel and Pfeiffer). 



media the tubercle bacillus which he uses for making 

 tuberculin still kills guinea-pigs in three weeks after 

 intraperitoneal inoculation. 



It is really surprising to note the extremely simple 

 compounds in which the tubercle bacillus can be grown. 

 Instead of requiring the most concentrated albuminous 

 media, as was once supposed, Proskauer and Beck 1 have 

 shown that the organism can grow in non-albuminous 

 media containing asparagin, and that it can even be in- 



1 Zeitschrift fur Hygiene, August io, 1894, xviii., No. I. 



