278 TUBERCULOSIS 



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, 

 however, 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. More- 

 over, 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 organ- 

 isms is constantly being added to, but the following may be 

 mentioned as examples : 



Moellers Grass Bacilli I. and II. The former was found in infusions 

 of Timothy-grass (Phleum pratense). It is extremely acid-fast, morpho- 

 logically resembles the tubercle bacillus, and in cultures may show club 

 formation and branching. The lesions produced closely resemble 



