40 BACTERIOLOGY. 



may be presented to the contrary is based upon untrust- 

 worthy methods of observation. 



Not infrequently bacteria 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 bacteria. (See Fig. 6.) 



FIG. 6. 



Zoogloea of bacilli. 



Very short oval bacilli may sometimes be mistaken 

 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 

 illumination from the reflector of the microscope with 

 which they are examined be 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 most reliable differential points, 

 however, are: the infallible property possessed by the 

 spores of developing into bacilli, and that of the spher- 

 ical organism with which they may have been con- 



