CHAPTER XVIII 



THE TUBERCLE BACILLUS AND OTHER ACID-FAST 



ORGANISMS 



IT is estimated that in the United States 160,000 persons 

 die each year of tuberculosis. For centuries the disease has 

 been recognized, but only within comparatively recent times 

 has its infectiousness been scientifically established. The fact 

 that tuberculosis might be induced by inoculation with tuber- 

 culous material was demonstrated by Villemin in 1865. Baum- 

 garten early in 1882 described the bacilli in tissue sections, but it 



remained for Robert Koch to 

 isolate the organism, to grow 

 it in pure culture, and with the 

 pure culture to reproduce the 

 characteristic lesions in ani- 

 mals. Koch announced his 

 discovery in 1882 and in 1884 

 he submitted his full report. 



Morphology and Staining. 

 Tubercle bacilli appear as 

 slender, non-motile rods about 

 2 p to 4 p in length and 0.3 



FIG. 28. Tubercle Bacilli. i\ r -1,1 T i i 



to 0.5 /* m 'width. In colored 



preparations they may appear straight or slightly curved, single 

 or lying together in heaps. Ordinarily they stain uniformly (Fig. 

 28). Frequently however, deeply stained thickenings are seen 

 which give to the organism a somewhat beaded appearance. At 

 first these granules were thought to be spores. Soon, however, 

 it was shown that the bacilli containing them were no more re- 



188 



