GROUPING. 39 



the body of the rods oval, glistening spores (see Fig. 4), 

 and, if the conditions are not altered, the rods may 

 entirely disappear, so that nothing be left in the cul- 

 ture 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 altera- 

 tions in their protoplasm which result in distortion of 

 their outline, and the appearance of the so-called " in- 

 volution forms." (See Fig. 5, a and 6.) In all of 



FIG. 5. 

 ' ft 



A i * 



;// < 



* s 



a b 



a. Spirillum of Asiatic cholera (comma bacillus). &. Involution forms of 

 this organism as seen in old cultures. 



these conditions, however, so long as death has not 

 actually occurred, it is possible under favorable condi- 

 tions to cause these forms to revert to the rod-shaped 

 ones from which they originated. 



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 bacilli 

 from micrococci or vice versa, and any evidence which 

 may be presented to the contrary is based upon untrust- 

 worthy methods of observation. 



