GROUPING. 61 



for micrococci, and at times micrococci in the stage of 

 segmentation into diplococci may be mistaken for short 

 bacilli ; but 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 noticeable if the illu- 

 mination of the microscope be reduced to the smallest 

 possible bundle of light-rays. The spores, moreover, 

 take up staining-reagents much less readily than do 

 the micrococci. The most reliable differential points, 

 however, are the infallible properties possessed by the 

 spores of developing into bacilli, and by the spherical 

 organism with which they may have been confounded 

 of always producing other micrococci of the same 

 spherical form. 



A convenient classification of bacilli is that based 

 upon constant characteristics which are seen to ap- 

 pear in the course of their development under spe- 

 cial conditions certain of them possessing the power 

 of forming spores, while from others this peculiarity 

 is absent. 



We have less knowledge of the life-history of the 

 spiral forms. Efforts toward their cultivation under 

 artificial conditions have thus far been successful in 

 only a comparatively limited number of cases. Mor- 

 phologically, they are thread- or rod-like bodies which 

 are twisted into the form of spirals. In some of them 

 the turns of the spiral are long, in others quite short. 



