BACTERIUM TUBERCULOSIS. 349 



in the conditions under which one endeavors to isolate 

 bacillus tuberculosis from the tissues may cause total 

 failure. It is, therefore, necessary that the injunctions 

 for obtaining it in pure culture should be carefully 

 observed. 



PREPARATION OF CULTURES FROM TISSUES. Under 

 strictest antiseptic precautions remove from the animal 

 the diseased organ 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 without attempting to break it up or 

 smear it over the surface, leave it for four or five days 

 in the incubator. After this time it may be rubbed 

 over the surface of the serum. The object of this is to 

 give to the bacilli in the nodule an opportunity to 

 multiply, under the favorable conditions of temperature 

 and moisture, before an effort is made to distribute them 

 over the surface of the medium. 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 extraneous saprophytic 

 organisms during the 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 



