CULTURES FROM TISSUES. 213 



this in turn is sealed up and retained at the same tem- 

 perature. Once having obtained the organism in pure 

 culture its subsequent cultivation may be conducted 

 upon the glycerin-agar-agar mixture— ordinary neutral 

 nutrient agar-agar to which 6 or 7 per cent, of glycerin 

 has been added. This is a very favorable medium for 

 the growth of this organism after once having estab- 

 lished its saprophytic form 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 infu- 

 sion bouillon to which 6 or 7 per cent, of glycerin has 

 been added. 



In appearance the cultures of the tubercle bacilli are 

 characteristic — 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 

 clumps of mealy-looking granules. They are never 

 moist, and frequently have the appearance of coarse 

 meal which had been spread upon the surface of the 

 medium. In the lower part of the tube in which they 

 are growing (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. 



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 



10* 



