GROUPING. 39 



ing within the body of the rods oval, glistening spores 

 (see Fig. 4), 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. 4, c 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. 5, a and 6). In 



Fig. 5. 





a b 



a. Spirillum of Asiatic cholera (comma bacillns). 6. Involntion forms of 

 this organism as seen in old cultures. 



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

 not actually occurred, it is possible to cause these forms 

 to revert to the rod-shaped ones from which they orig- 

 inated, by the renewal of the conditions favorable to 

 their normal vegetation. 



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 

 of the morphology of the members of one group into 

 that of another — that is, one can never produce baciUi 

 from micrococci, or vice versa, and any evidence which 



