INVOLUTION: ATTENUATION 27 



in a new genus Mycobactcriitin or Tnbcrciiloinyccs, and the diphtheria para- 

 site in another, Coryncbactcrimn. In the writer's opinion such an alteration 

 is not justified, for the branched forms of tubercle bacillus that arise in three 

 to six months old colonies arc by no means common, and agree closely in 

 appearance with the involution forms in the root-nodules of leguminosae 

 Fig. 14, e-f, and of the acetic bacteria 'Fig. 14, c-d. 



If the influences which give rise to involution forms be restrained 

 within certain limits, a general weakening or attenuation of the bacteria is 



!" Hi. 14. Involution forms, a, Bac. siibtilis from a four-days old culture containing i % sal ammoniac, 2 / grape 

 sugar, and 0-5 % nutritive salts (weakly acid), b, Typhoid-like bacilli from water in hay infusion with 4 % sal 

 ammoniac; they are non-motile, without cilia, and suggestive of the bacteria of root-nodules (e and_/\ c, Bac- 

 terium aceti at 3Q-4l (from E. Chr. Hansen). d, Bacterium Fasteurianum, 7 hours at 34 (from Hansen). e, Bac- 

 teroids from the root-nodules of Vicia villosa \ the round spots are the still retainable remnants of cell-contents (from 

 Morck). f, Bacteroids from Lupinus albtis (from Morck ; the four-armed one is from Vicia villosa). r, Tubercle 

 bacillus, branched filament from sputum (from Coppen Jones). //, Diphtheria bacilli, so-called branched forms ; 

 they are certainly involution forms (from Bernheim and Folger). Magn. a and b 1500, c and d 100, e and /about 

 1500,^ 1250, It about 100. 



effected. This condition arises spontaneously in long-continued cultivation 

 on artificial media ; virulence, fermentative power, and other functions being 

 diminished. They may be revived again, however, if the process has 

 stopped short of involution, by restoring the bacteria to a more natural 

 environment: in the pathogenic species 'by repeated passage through the 

 animal body, in the ferment organisms by giving them renewed oppor- 

 tunity for active fermentation. 



The attenuation induced by prolonged artificial culture can be secured 

 in a much shorter time by exposure to more noxious agencies. The most 

 important form of enfceblement, the loss of infectious power, can be induced 



