252 TUBERCULOSIS 



undergo no multiplication when injected into the tissues of 

 mammals, and attempts to modify this characteristic have so 

 far been unsuccessful. Weber and Taute have cultivated this 

 organism from mud, and also from organs of healthy frogs. It 

 is thus probably to be regarded as a saprophyte which is only 

 occasionally associated with disease in the fish. According to 

 the results of different experimenters it is possible to modify 

 human tubercle bacilli by allowing them to sojourn in the tissues 

 of cold-blooded animals, e.g. the frog, blind-worm, etc., so that 

 they flourish at lower temperatures. These results have, how- 

 ever, been recently called in question, as it has been stated the 

 organisms obtained were not modified tubercle bacilli but other 

 acid-fast bacilli which may be found in the tissues of normal 

 cold-blooded animals. This question must accordingly be 

 considered still an open one. 



All the above facts taken together indicate that tubercle 

 bacilli may become modified in relative virulence and in con- 

 ditions of growth by sojourn in the tissues of various animals. 

 This modification appears slight, though of definite character in 

 the case of bovine tuberculosis, more distinct in the case of 

 avian tuberculosis, and much more marked, if not permanent, in 

 the case of fish tuberculosis, that is, of course, in their relations 

 to the bacilli from the human subject. 



Other Acid-fast Bacilli. Within recent years a number of 

 bacilli presenting the same staining reaction as the tubercle 

 bacilli have been discovered. Such bacilli have a comparatively 

 wide distribution in nature, as they have been obtained from 

 various species of grass, from butter and milk, from manure, and 

 from the surfaces of animal bodies. Microscopically, they agree 

 more or less closely with tubercle bacilli, though most of them 

 are shorter and plumper ; many of them show filamentous and 

 branching forms under certain conditions of culture. Moreover, 

 on injection, they produce granulation-tissue nodules which may 

 closely resemble tubercles, although on the whole there is a 

 greater tendency to softening and suppuration, and usually the 

 lesions are localised to the site of inoculation. The most im- 

 portant point of distinction is the fact that their multiplication 

 on artificial media is much more rapid, growth usually being 

 visible within forty-eight hours and often within twenty-four 

 hours at 37 C. Furthermore, in most instances, growth occurs 

 at the room temperature. The general character of the cultures 

 in this group is a somewhat irregular layer, often with wrinkled 

 surface, dry or moist in appearance, and varying in tint from 

 white to yellow or reddish brown. The number of such 



