XON-SPORING BACILLI 273 



THE TUBERCLE BACILLUS. 



This bacillus is the cause of tuberculosis, an infective 

 disease, characterized by lesions which are nodular bodies 

 called " tubercles," or by diffuse infiltrations of tuberculous 

 tissue, which may undergo caseation and finally ulcerate, 

 or may become sclerosed, and in some cases calcified. 

 The infectious nature of tuberculous material was for long 

 suspected, was proved by Villemin in 1865, and by Armanni 

 and Cohnheim and Salomonsen from 1870 to 1880, 

 Baumgarten first described the bacillus in sections, but 

 Koch first established its causal nature on a solid basis 

 by : (i) Demonstrating the presence of the tubercle 

 bacillus in a great variety of tissues and organs ; (2) Pre- 

 paring pure cultures of the organism from these ; 

 (3) Producing the disease by the inoculation of the bacillus 

 derived from pure culture ; and (4) Recovering the same 

 organism from the diseased parts of inoculated animals. 

 These four articles are known as Koch's postulates, and 

 all of them have to be satisfied before an organism 

 can be absolutely proved as the cause of a specific 

 disease. At present, for quite a number of bacteria, 

 some of these postulates have yet to be fulfilled as 

 regards mankind. 



Description. Bacillus tuberculosis is a slender rod, often 

 slightly curved, measuring 2-5 to 3-5 micra long by 0-3 

 micron in width. They are of uniform thickness, or may 

 show slight swelling at the ends or even in their length. 

 They may lie singly in the tissues or sputum, but often in 

 small heaps or masses. In cultures, a remarkable fila- 

 mentous growth has been repeatedly observed. In the 

 sputum, long branching hypha-like filaments, sometimes 

 with swollen ends, have been found. These are looked 

 upon by some bacteriologists as involution forms, but many 

 regard them as evidence of the relationship of the tubercle 

 bacillus to the hyphomycetes. A capsular or enveloping 

 substance is produced by the bacillus, more by the human 

 form than by the bovine, and more the longer the growth 

 on blood serum. When stained, the bacillus often appears 

 beaded, the unstained spaces being regarded as vacuoles 

 by some and as spores by others. Inasmuch as the bacilli 



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