XL] 



BACILLUS: PATHOGENIC FORMS. 



165 



In all cases of human tuberculosis, particularly in the 

 sputum, in caseating scrofulous glands, in bovine tubercles, in 

 artificially-induced tubercles and caseating glands of rodents, 

 the tubercle-bacilli have been shown to exist. They are 

 most numerously found in the caseous masses in the lung 

 found in bovine tuberculosis. Here Koch found them not 

 only scattered through the caseous masses, but also in the 

 well-known giant-cells ; in some cases they form a more or 

 less regular zone in the peripheral portion of the cell. But 



FIG. 90. FROM A SECTION THROUGH TUBERCULOUS DEPOSITS IN THE LUNG OF 



A Cow. 



Two giant-cells and two small cells containing tubercle-bacilli. 

 Magnifying power 700. 



according to Koch the bacilli by and by disappear again from 

 the giant-cells. 



The bacilli do not show any motility and often include 

 granules considered to be spores ; they thus would be capable 

 of forming spores within the body. Owing to these, human 

 phthisical sputum retains its virulence even after drying. 

 Koch cultivated the bacilli artificially, i.e. outside the body, 

 and by carrying on the cultivation for several successive trans- 

 missions succeeded in isolating and clearing them from the 



