XIV] BACILLUS TUBERCULOSIS 349 



bacilli have been published, which are all good to a lesser 

 or greater degree, but the one just mentioned is as good 

 and in many instances has proved simpler and better. The 

 tubercle bacilli always occur in tubercular nodules, more 

 numerously where caseation has already set in than in the 

 earlier stages. They occur isolated or in groups between 

 the cells constituting the tubercle, or they are found singly 

 or in small groups within the larger cells ; when present in 

 giant cells they are found in large numbers forming a sort 

 of zonular ring around the central portion (see Figs. 133 

 and 134). In some giant cells their number is sometimes 

 very limited, and Koch has concluded from this fact that 

 the tubercle bacilli suffer death in the giant cells and hence 

 disappear from them. In human tubercle the tubercle 

 bacilli are, as a rule, between the elements constituting the 

 tubercle, but as just mentioned they also occur within the 

 cells uni- and multi-nucleated. In bovine tubercle, however, 

 the rule is that they are mostly present in the uni- and multi- 

 nuclear cells, and only when these degenerate and break 

 up do they become free ; in the caseous matter they are 

 present in groups in the granular ddbris. In tubercle of 

 rabbit (lung and liver) produced by inoculation with bovine 

 tubercular matter, or with artificial culture derived from 

 bovine tubercle, the presence of tubercle bacilli within the 

 cells — small, large, and giant cells — is very conspicuous, 

 and yields very remarkable specimens (see Fig. 136). 



The tubercle bacilli in human tubercle are delicate 

 cylindrical rods measuring i'5-4 it-; many are straight, with 

 rounded ends, but others are slightly curved ; in pre- 

 parations (sputum, purulent matter or sections) stained in 

 the above manner the bacilli always appear composed of 

 granules, that is to say, within a faintly stained sheath the 

 protoplasm is segregated into deeply stained, cubical, spheri- 



