THE STRUCTURE OF BACTERIA, II 



a. Coccus-forms, comprising spherical and 

 ellipsoid cells. 



b. Rod-shaped forms, plainly elongated in 

 one direction. These may be distinguished 

 according to their length as long or short rods. 

 Many rods have an approximately uniform 

 diameter throughout and the ends may be 

 either rectangular in outline or more or less 

 rounded. In some rods the diameter of the 

 cell varies in different portions so as to 

 produce a spindle-shaped or club-shaped cell, 

 or one fashioned like a pestle, or a whetstone 

 or a drumstick. Rods may be rigid or flexi- 

 ble, and, in the latter case, often appear curved. 



c. Corkscrew forms, comprising all spirally 

 twisted cells. The smallest forms often resem- 

 ble rods bent with a comma-like flexure. The 

 screws may be rigid or flexible, of equal diam- 

 eter throughout, or varying in diameter at dif- 

 ferent points. 



Each bacterial cell is able to maintain an 

 independent existence, and frequently exhibits 

 transition forms in the course of its own 

 development. A sphere elongates into an 

 ellipsoid ; a long rod stretches out, divides and 

 becomes two short rods ; a short rod or spiral 

 divides into two ellipsoids or spheres. Before 

 division, the individual cells as a rule elongate, 

 and their forms become thereby more clearly 



