358 BACTERIOLOGY. 



tidal cultures from the animal body are offsprings of 

 the more saprophytic varieties. At best, one never sees 

 with the tubercle bacillus a saprophytic condition in 

 any way comparable to that possessed by many of the 

 other organisms with which we have to deal. 



For the cultivation of bacillus tuberculosis directly 

 from the tissues of the animal, the method by which one 

 obtains the best results is that recommended by Koch, 

 viz., cultivation upon blood-serum. Its parasitic ten- 

 dencies are so pronounced that even very slight variations 

 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 



