260 BACTERIOLOGY. 



tion upon blood-serum. So strictly is this organism a 

 parasite that very limited alterations in the conditions 

 under which it is growing may result in failure to suc- 

 cessfully study it. It is, therefore, necessary that the 

 injunctions for obtaining it in pure culture should be 

 carefully observed. 



The blood-serum upon which the organism is to be 

 cultivated should be comparatively freshly prepared — 

 that is, it should not be dry. 



Peepaeation of Cultures from Tissues. — 

 Under strictest antiseptic precautions, remove from the 

 animal the tubercular tissue — the liver, spleen, or a 

 lymphatic gland being preferable. Place the tissue in 

 a sterilized Petri dish and dissect out with sterilized 

 scissors and forceps the small tubercular nodules. Place 

 each nodule upon the surface of the blood-serum, one 

 nodule in each tube, and with a heavy, sterilized, looped 

 platinum needle or spatula, rub it carefully over the 

 surface. It is best to dissect away twenty to thirty such 

 tubercles and treat each in the same way. Some of the 

 tubes will remain sterile, others may be contaminated by 

 outside organisms during the manipulation, while a few 

 may give the result desired — a growth of the bacilli 

 themselves. 



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 



