66 BACTERIOLOGY 



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 mor- 

 phology of the members of one group into that of another — 

 that is, one can never produce bacilli from micrococci, nor 

 vice versa; and any evidence which may be presented to 

 the contrary is based upon untrustworthy methods of 

 experimentation. 



Very short oval bacilli may sometimes be mistaken for 

 micrococci, and at times micrococci in the stage of segmenta- 

 tion into diplococci may be mistaken for short bacilli; but 



Fig. 5 





<r. A 



[■t'l'^ 



a, spirillum of Asiatic cholera (comma bacillus); normal appearance 

 in fresh cultures; b, involution-forms of this organism as seen in old cul- 

 tures. 



by careful inspection it will always be possible to detect a 

 continuous outline along the sides of the former, and a 

 slight transverse indentation or partition-formation between 

 the segments of the latter. The high index of refraction of 

 spores, the property which gives to them their glistening 

 appearance, will always serve to distinguish them from 

 micrococci. This difference in refraction is especially notice- 

 able if the illumination of the microscope be reduced to the 

 smallest possible bundle of light-rays. The spores, more- 

 over, take up staining-reagents much less readily than 

 do the micrococci. The most reliable differential points, 



