TUBERCLE 153 



fated to receive several names: Bacillus tuberculosis ^ Koch, 1884, Sclerothrix. 

 KocJiii, Metschnikoff, 1889, Mycobacterium tuberculosis, Lchmann and 

 Neumann, 1896, Tiibcrcnloinyccs. Coppen Jones, 1896. It is a delicate, 

 slender rod, often slightly curved, non-motile. The average size is from 

 1-5 n to 4 M long by 02 /u, to 0-4/1 thick, but it is extremely variable in 

 length and thickness, both in the tissues and in cultures, in both of which 

 situations it sometimes appears in a filamentous form. On culture media 

 it gives rise to thick, opaque, scaly or wrinkled membranous colonies of dry 

 consistence. In consequence of the small size of the cell its finer structure 

 cannot be seen in detail (136). The cell contents, however, would seem to 

 be denser than those of other bacilli, for the tubercle bacillus is much more 

 highly refracting than any other species. It further differs from other 

 bacteria in containing a large amount of true cellulose in its cell-wall. It is 

 the greater density of the cell that enables it to retain anilin dyes with such 

 tenacity, a fact that facilitates immensely the detection of the bacillus in 

 tuberculous material. In very old cultures, and sometimes in sputum, the 

 bacilli often appear as dotted, strongly-stained granules alternating with 

 colourless spaces (Fig. 28,^-). We have already seen that this occurs in the 

 diphtheria bacillus. In both cases it indicates a degeneration, and must 

 not be regarded as a specific structure as a sign of sporulation, for 

 instance. Real spores are not yet known. The tubercle bacillus shows 

 sometimes also another sign of the discomfort that genuine parasites 

 undergo in artificial cultures. Involution forms arise swollen rods and 

 feebly-branched filaments reminiscent of the bacteroids of Leguminosae 

 (Fig. 14, ), which have by some investigators been wrongly regarded as 

 having morphological and systematic importance*. 



Closely resembling the tubercle bacillus is the bacterium which is 

 presumably the cause of leprosy. It has not been obtained as yet in pure 

 cultures. 



The bacteria already described can all be distinguished by their 

 morphological characters, doubtful cases being confirmed by experiments 



* The translator's observations do not permit him to agree with this view. According to his 

 investigations (Centr. f. Bakt., 1895', corroborated since by many other observers, the ramifications 

 of the tubercle filaments are examples of true branching, and, together with the many other points 

 of resemblance to Actinomyces, justify us in placing the organism among the filamentous fungi. The 

 suggestion made in 1895, that a saprophytic form of the bacillus would probably be found outside 

 the animal body, has also been fulfilled through the discovery, by Moeller (Therapeut. Monatsheftc, 

 Nov. 1898), of a bacillus almost indistinguishable fiom the tubercle bacillus growing upon Timothy- 

 grass. Several other snprophytic and parasitic organisms having the closest resemblance to Koch's 

 ' bacillus,' but growing at low temperatures, have now been described, and leave little room for 

 doubt that they, together with the organisms of mammalian and avian tuberculosis, are closely 

 related members of the same family. They show branched filaments in cultures, and when injected 

 into the living tissues most of them give rise to actinomycosis-like centres of radiating filaments, 

 terminating in clubbed ends (Zeitschr. f. Hygiene, vol. xxi, 1899). 



