MORPHOLOGY. 81 



It must be borne in mind, however, 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 inaccu- 

 rate methods of work. 



Not infrequently bacilli may be observed irregularly 

 massed together as a pellicle. When in this condition 

 they are held together by a gelatinous material, and are 

 known as zoogloea of bacilli. 



Very short oval bacilli may sometimes be mistaken for 

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

 tation into diplococci may be mistaken for short bacilli ; 

 but by careful inspection it will always be possible to de- 

 tect a continuous outline along the sides of the former 

 and a slight transverse indentation or partition-forma- 

 tion 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 will be especially noticed if the illumination 

 from the reflector of the microscope w r ith which they are 

 to be examined is reduced to the smallest possible bundle 

 of light-rays. The spores, moreover, take up the staining 

 reagents much less readily than do the micrococci. The 

 crucial test, however, is the property, in the case of the 

 spores, of growing out into bacilli; and of the spherical 

 organism with which it has been confounded, of develop- 

 ing only into another micrococcus of the same round 

 form. 



For convenience, a common classification of the bacilli 



