170 PATHOGENIC BACTERIA. 



nature of this disease would be proved, and some, as 

 Klebs, Villemin, and Cohnheim, were "within an ace" 

 of the discovery, it remained for Robert Koch to succeed 

 in demonstrating and isolating the specific bacillus, now 

 so well known, and to write so accurate a description of 

 the organism and the lesions it produces as to render it 

 almost unparalleled in medical literature. 



The tubercle bacillus (Fig, 54) is a rod-shaped organ- 



FIG. 54. Section of a peritoneal tubercle from a cow, showing the tubercle 

 bacilli; x 500 (Frankel and Pfeiffer). 



ism with rounded ends and a slight curve, measuring 

 from 1.5-3.5 p in length and from 0.2-0.5 // in breadth. 

 It very commonly occurs in pairs, which may be asso- 

 ciated end to end, but generally overlap somewhat and 

 are not attached to each other. It is very common to 

 observe a peculiar beaded appearance in organisms found 

 in pus and sputum (Fig. 55), due to the contraction of 

 fragmented protoplasm within the resisting capsule (?). 

 By some these fragmentations are thought to be bacilli 

 in the stage of sporulation. Koch originally held this 

 view himself, but researches have not been able to sub- 

 stantiate the opinion, and at present the evidences pro 



