368 A MANUAL OF BACTERIOLOGY 



follow that is, lime -salts are deposited and the nodule 

 is converted into a calcareous mass. 



So far back as 1865 Villemin showed that inoculation of 

 rabbits with human caseous material was followed by a 

 development of nodules similar in all respects to the 

 miliary tubercles in man. Cohnheim, Burdon Sanderson, 

 and Wilson Fox confirmed this observation, and it was 

 subsequently shown that non-tuberculous matter is 

 unable to set up tuberculosis. Tuberculosis was thus 

 proved to be inoculable and to be a specific infective 

 disease, and attention was next directed to the discovery 

 of the causative micro-organism. In 1882 Koch 

 announced that he had found a special bacillus, the 

 tubercle bacillus, in tuberculous tissues, which could be 

 isolated and cultivated, and which reproduced the disease 

 on inoculation. 



The Tubercle Bacillus 



Morphology. The tubercle bacillus (B. [Mycobacterium] 

 tuberculosis) is a slender rod, often slightly curved, and 

 averaging 2-3 p, in length, though the length varies in 

 sputum and in the tissues from 1-5 /x to 6-5 ^ ; in cultures 

 it tends to be short, on serum being about 1 /x to 2 /x. In 

 stained preparations one or more unstained intervals are 

 often seen in the rods (Plate IX, a), which are considered 

 by some observers to be spores, but spores are single and 

 not multiple, and are regular spherical or ovoid bodies, 

 whereas the unstained spaces in the tubercle rods are 

 irregular. Moreover, in the same specimen of sputum 

 the amount of " beading," varies with different staining 

 methods (Plate IX, b) ; in a preparation stained by 

 Gram's method it is usually more pronounced than in 

 one stained with carbol-fuchsin. It is probable, there- 

 fore, that the beading is partly due to segmentation of 

 the protoplasm, and is partly an artifact due to the staining 



