CHAPTER XXXIII 

 THE TUBERCLE BACILLUS 



IN view of the clinical manifestations of tuberculosis, it is not sur- 

 prising that the infectious nature of the disease has been suspected for 

 many centuries. Even Fracastor had remarkably modern ideas concern- 

 ing its transmission. Inoculation by means of tuberculous material was 

 first successfully accomplished by Klencke, in 1843, and, more elabo- 

 rately, by Villemin, 1 in 1865. It was not until 1882, however, that 

 Koch 2 succeeded in isolating and cultivating the tubercle bacillus. 

 Baumgarten 3 had previously seen the bacillus in tissue sections, but his 

 researches were limited to purely morphological observations. Koch, 

 in addition to demonstrating the bacillus in tuberculous tissues from 

 various sources, produced characteristic lesions in guinea-pigs and other 

 animals by infecting them with pure cultures, and established beyond 

 doubt the etiological relationship of the bacillus to the disease. 



Morphology. Tubercle bacilli appear as slender rods, 2 to 4 micra 

 in length, 0.2 to 0.5 micra in width. Their ends are usually rounded. 

 The rods may be straight or slightly curved; their diameters may be 

 uniform throughout; more often, however, they appear beaded and 

 irregularly stained. The beaded appearance is due to different causes. 

 Unstained spaces may occur along the body of the bacillus, especially 

 in old cultures. These are generally regarded as vacuoles. The bodies 

 of the bacilli, on the other hand, may bulge slightly here and there, often 

 in three or four places, showing oval or rounded knobs which stain with 

 great depth and are very resistant to decolorization. These thickenings 

 were formerly regarded as spores, but in view of the fact that the bacilli 

 are not more resistant against heat and disinfectants than other vegeta- 

 tive forms, this interpretation is probably incorrect. The bacilli are said 

 to possess a cell membrane which confers upon them their resistance 

 against drying and entrance of stains. This membrane gives a cellulose 

 reaction and is believed to contain most of the waxy substances which 

 can be extracted from the cultures. 



1 Villemin, Gaz. hebdom., 1865. 



2 Koch, Berl. klin. Woch., 1882; Mitt. a. d. kais. Gesundheitsamt, 1884. 



3 Baumgarten, Virchow's Arch., Ixxxii. 



479 



