20 



THE NATURE OF BACTERIA. 



This process is called fission and hence these organisms 

 are the Fission fungi. This group includes the organisms 

 which have for the last quarter of a century been known 

 as Bacteria. It is with these that we are chiefly concerned 

 in this work. 



II. FORM AND CLASSIFICATION OF BACTERIA OR 

 SCHIZOMYCETES. 



Under ordinary conditions Bacteria are extremely simple 

 in form. Long ago they were compared to billiard balls, 

 lead pencils and cork screws (Fig. 4), and even the most 



FIG. 4. 



General shape of bacteria : a, spheres ; b, rods; c, spirals. 



careful work with the modern microscope has hardly im- 

 proved upon this somewhat crude but striking comparison. 

 Nearly all bacteria are either spheres, cylindrical rods of 

 greater or less length, or spiral rods. In size they are in- 

 conceivably minute, being by far the smallest living organ- 

 isms known, and demanding the highest powers of the micro- 

 scope for their study. The spheres, for example, have a 

 diameter varying from .25 fj. to 1.5 ft (0.000012 to 0.00006 

 inch). The rods have a diameter of about the same dimen- 

 sions, but their length may be considerably greater, espe- 

 cially when they grew into long slender threads. All are, 

 ho.wever, far below the limits of human vision unaided by 

 the microscope. 



