BACILLUS OF TUBERCULOSIS. 289 



bacilli themselves. It also contains all the albuminoid 

 and other materials originally contained in the bouillon 

 which have remained unaffected by the activities of the 

 bacilli. There are two preparations known respec- 

 tively as the old and the new tuberculin. 



Old tuberculin is prepared as follows : The tubercle 

 bacillus is cultivated in an infusion of calf s flesh, or of 

 beef flesh, or extract to which 1 per cent, of peptone 

 and 4 to 5 per cent, of glycerin have been added, the 

 culture liquid being slightly alkaline. The inoculation 

 is made upon the surface from a piece of very thin 

 pellicle from a young bouillon culture, or, if the bou- 

 illon culture is unobtainable, with small masses from a 

 culture on glycerin-agar. These masses, floating on 

 the surface, give rise in from three to six weeks, accord- 

 ing to the rapidity with which the culture grows, to an 

 abundant development and to the formation of ,a toler- 

 ably thick and dry, white crumpled layer, which finally 

 covers the entire surface. At the end of four to eight 

 weeks development ceases, and the layer after a time 

 sinks to the bottom. Fully developed cultures, after 

 having been tested for purity by a microscopical exami- 

 nation, are passed into a suitable vessel and evaporated 

 to one-tenth of their original bulk over a water-bath 

 at a temperature of 70 to 80 C. The liquid is then 

 filtered through chemically pure sterilized filter-paper. 

 The crude tuberculin thus obtained contains 40 to 50 per 

 cent, of glycerin and keeps well, retaining its activity 

 indefinitely. 



The method of treatment and the results obtained 

 from the old tuberculin have been described recently 

 by Koch briefly as follows : After each injection, which 

 should be large enough to cause a slight but not a great 



19 



