PREPARATION OF CULTURES FROM TISSUES. 279 



has been added. This is a very favorable medium for 

 the growth of this organism after it has accommodated 

 itself to its saprophy tic mode of existence, though blood- 

 serum is perhaps the best medium to be employed in 

 obtaining the first generation of the organism from the 

 tubercular 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 6 or 7 per cent, of glycerin. 



Cultures of the tubercle bacillus are characteristic in 

 appearance after once having seen them there is but 

 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 

 lumps of mealy-looking granules. They are never 

 moist, and frequently have the appearance of coarse 

 meal which has been 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 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 making up the growth adhere so 

 tenaciously together that it is with the greatest difficulty 

 that they can be completely 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 on glycerin-agar-agar. 



