BACTERIUM TUBERCULOSIS 443 



If these primary efforts result in a growth of the bacilli, 

 further cultivations may be made by taking up a bit of 

 the colony, preferably a moderately large quantity, and 

 transferring it to fresh serum, and this in turn is sealed 

 up and retained at body temperature. Once having ob- 

 tained the organism in pure culture, its subsequent culti- 

 vation may be conducted upon the glycerin-agar-agar 

 mixture ordinary neutral nutrient agar-agar to which 

 from 4 to 6 per cent, of glycerin has been added. This is 

 a very favorable medium for the growth of this organism 

 after it has accommodated itself to its saprophytic mode 

 of existence, though blood serum is perhaps the best medium 

 to be employed in obtaining the first generation of the 

 organism from tuberculous tissues. 



The organism may be cultivated also on neutral milk 

 to which 1 per cent, of agar-agar has been added, also upon 

 the surface of potato, and likewise in meat-infusion bouillon 

 containing from 4 to 6 per cent, of glycerin. 



Cultures of the tubercle bacillus are characteristic in 

 appearance once having seen them there is little proba- 

 bility of subsequent mistake. They appear as dry masses, 

 which may develop upon the surface of the medium either 

 as flat scales or as coarse, heaped up, granular nesses. 

 They are never moist, and frequently have the appearance 

 of dry meal spread upon the surface of the medium. In 

 the lower part of the tube in which they are growing i. e., 

 that part occupied by a few drops of fluid which has in part 

 been squeezed from the medium during the process of solidi- 

 fication, and is in part water of condensation the colonies 

 may be seen to float as a thin pellicle upon the surface of the 

 fluid. 



The individuals composing the growth adhere so tena- 



