38 BACILLUS TUBERCULOSIS 



introduced considerable stress was laid on this 

 increase in saprophytic character, but, though some 

 modification undoubtedly occurs, yet part of the 

 effect attributed to the medium was due to the 

 fact that B. tuberculosis avium was employed for 

 cultivation, and this is now recognised as being a 

 distinct variety differing considerably from the 

 mammalian tubercle bacillus. 



In culture (Fig. 29) the bacillus presents almost 

 the same morphological characters and staining 

 reactions as when in the sputum. The beading, 

 though not so regular, is nearly equally marked, 

 but the fine slender bacillus becomes, as a rule, 

 thicker and coarser, and often presents enlarged 

 extremities. 



Under certain conditions long branched forms 

 appear in the culture, which resemble closely the 

 forms which are shown in Fig. 14. These forms 

 have been studied by Coppen Jones, Babes, and 

 others, and are usually an evidence of saprophytic 

 life and small virulence. 



Fig. 34 is a photograph of a section through a 

 tubercular nodule stained with fuchsine and methy- 

 lene-blue. The centre of the field is occupied by 

 the characteristic giant cell, with the pale un- 

 differentiated central portion of necrosed caseating 



