PREPARATIONS OF CULTURES FROM TISSUES. 277 



the bacilli taken directly from the animal body grow 

 only very imperfectly, or in many cases, not at all. 

 From this it seems probable that there is a difference 

 in the nature of individual tubercle bacilli some ap- 

 pearing to be capable only of growth in the animal 

 tissues, while others are apparently possessed of the 

 power to lead a limited saprophytic existence. It may be, 

 therefore, that those bacilli which we obtain as artificial 

 cultures from the animal body are offsprings from 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. 



In efforts to cultivate this organism directly from the 

 tissues of the animal, the method by which one obtains 

 the best results is that recommended by Koch, viz., culti- 

 vation 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. 



PREPARATION 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 



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