GROUPING. 61 



found — the anthrax bacillus and bacillus subtilis are 

 conspicuous examples of this. Again, under certain 

 conditions, many of them possess the property of form- 

 ing within the body of the rods oval, glistening spores 

 (see Fig. 6), and, if the conditions are not altered, the 

 rods may entirely disappear and nothing be left in 

 the culture but these oval spores. In some of them 

 this phenomenon of spore-formation is accompanied by 

 an enlargement or swelling of the bacillus at the point 

 at which the spore is located (see Fig. 5, e and d). 

 Again, many of them, from unfavorable conditions of 

 nutrition, aeration, or temperature, undergo pathological 

 changes — that is, the individuals themselves experience 

 degeneration of their protoplasm with coincident dis- 

 tortion of their outline ; they are then usually referred 

 to as "involution-forms" (see Fig. 6, a and 6). In 



Fig. 6. 





/'i 



a. Spirillum of Asiatic cholera (comma bacillus) ; normal appearance 

 in fresh cultures. 5, Involution-forms of this organism as seen in old 

 cultures. 



all of these conditions, however, so long as death has 

 not occurred, it is possible to cause these forms to revert 

 to the typical rods from which they originated, by the 

 renewal of conditions favorable to their normal vege- 

 tation. 



It must be borne in mind, though, that it is never 

 possible by any means to bring about changes in these 

 organisms that will result in the permanent conversion 



