THE TUBERCLE BACILLUS. 343 



organisms during tlie manipulation, while a few may 

 give the result desired, viz., a growth of the tubercle 

 bacillus itself. 



The blood-serum upon which the organism is to be 

 cultivated should be comparatively freshly prepared — 

 that is, should not be dry. 



After inoculating the tubes they should be carefully 

 sealed to prevent evaporation and consequent dry- 

 ing. This is done by burning off the overhanging 

 cotton plug in a gas-flame, and then impregnating 

 the upper layers of the cotton with either sealing- 

 wax or paraffin of a high melting-point ; or by insert- 

 ing over the burned end of the cotton plug a soft, 

 closely fitting cork that has been sterilized in the 

 steam sterilizer just before using (Ghriskey). This 

 precaution is necessary because of the slow growth of 

 the organism. Under the most favorable conditions 

 tubercle bacilli directly from the animal body show no 

 evidence of growth for about twelve days after inocu- 

 lation upon blood-serum, and, as they must be retained 

 during this time at the body-temperature — 37.5° C. — 

 evaporation would take place very rapidly and the 

 medium would become too dry for their development. 



If these primary efforts result in the appearance of a 

 culture of the bacilli, further cultivations may be made 

 by taking up a bit of the colony, preferably a moder- 

 ately large quantity, and transferring it to fresh serum, 

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

 temperature. Once having obtained the organism in 

 pure culture, its subsequent cultivation may be con- 

 ducted upon the glycerin-agar-agar mixture — ordinary 

 jieutral nutrient agar-agar to which from 4 to 6 per cent, 

 of glycerin has been added. This is a very favorable 



