344 BACTERIOLOGY. 



medium for the growth of this organism after it has 

 accommodated itself to its saprophytic mode of exist- 

 ence, 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-infu- 

 sion 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 

 probability of subsequent mistake. They appear as 

 dry masses, which may develop upon the surface of 

 the medium either as flat scales or as coarse granular 

 masses. 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 groAving — i. e., that part occupied by a few drops of 

 fluid which has in part been squeezed from the medium 

 during the process of solidification, 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 

 tenaciously together that it is with the greatest diffi- 

 culty they can be separated. In even the oldest and 

 dryest cultures pulverization is impossible. The masses 

 can only be separated and broken up by grinding in 

 a mortar with the addition of some foreign substance, 

 such as very fine, sterilized sand, dust, etc. 



The cultures are of a dirty-drab or brownish-gray 

 color when seen on serum or glycerin-agar-agar. 



On potato they grow in practically the same way, 



