278 BACTERIOLOGY. 



tubes will remain sterile, others may be contaminated by 

 outside organisms during the manipulation, while a few 

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

 bacilli themselves. 



The blood-serum upon which the orgauism is to be 

 cultivated should be comparatively freshly prepared 

 that is, should not be dry. 



After inoculating the tubes they should be carefully 

 sealed up to prevent evaporation and consequent dry- 

 ing. This is done by burning off the superfluous 

 overhanging cotton plug in the gas-flame, and then im- 

 pregnating the upper layers of the cotton with either 

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

 inserting 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 inoculation 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 moderately 

 large quantity, and transferring it to fresh serum, and 

 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 



