BACILLI IN CHRONIC INFECTIOUS DISEASES. 381 



resisting power against heat than the bacilli themselves, would there- 

 fore simply be an admission that some bacteriologists had made a 

 mistaken inference based upon incomplete data. In view of the 

 facts stated we can simply repeat what was said at the outset, viz., 

 the question as to spore formation has not been definitely deter- 

 mined. 



The tubercle bacillus is a strict parasite, and its biological char- 

 acters are such that it could scarcely find natural conditions, outside 

 of the bodies of living animals, favorable for its multiplication. It 

 therefore does not grow as a saprophyte under ordinary circum- 

 stances. But it has been noted by Roux and Nbcard that when it 

 has been cultivated for a time in artificial media containing glycerin 

 it may grow in a plain bouillon of veal or chicken, in which media it 

 fails to develop when introduced directly from a culture originating 

 from the body of an infected animal. This would indicate the pos- 

 sibility of its acquiring the ability to grow as a saprophyte ; and we 

 can scarcely doubt that at some time in the past it was a true sapro- 

 phyte. The experiments of Nuttall indicate that the bacillus may 

 multiply, under favorable temperature conditions, in tuberculous 

 sputum outside of the body. And it is extremely probable that mul- 

 tiplication occurs in the muco-purulent secretion which accumulates 

 in pulmonary cavities in phthisical patients. In these cavities its de- 

 velopment may, in a certain sense, be regarded as saprophytic, as it 

 feeds upon non-living organic material. 



Koch first succeeded in cultivating this bacillus upon coagulated 

 blood serum, prepared as directed in Section VIII., Part First, of the 

 present volume. Roux and Nocard have since shown (1888) that it 

 grows very well on nutrient agar to which glycerin has been added 

 (six to eight per cent), and also in veal broth containing five per cent 

 of glycerin. It is difficult to obtain pure cultures from tuberculous 

 sputum, on account of the presence of other bacteria which grow 

 much more rapidly and take full possession of the medium before the 

 tubercle bacillus has had time to form visible colonies. For this rea- 

 son it is best to first inoculate a guinea-pig with the tuberculous spu- 

 tum and to obtain cultures from it after tuberculous infection has 

 fully developed. The inoculated animals usually die at the end of 

 three or four weeks. It is best to kill one which gives evidence of 

 being tuberculous, and to remove one or more nodules from the 

 lungs through an opening made in the chest walls. The greatest 

 care will be required to prevent contamination by other common 

 microorganisms. The instruments used must be sterilized by heat, 

 and the skin over the anterior thoracic wall carefully turned back ; 

 then, after again sterilizing knives and scissors, cut an opening into 

 the chest cavity, draw out the root of the lung, and take up with 



