24 GENERAL MORPHOLOGY 



simple condensation of the interior. The ordinary 

 animal or vegetable single cell 1 contains an easily dis- 

 tinguishable body, usually central, called the nucleus, 

 whose function it is to control the cell activities, 

 while the space between this body and cell wall is 

 occupied by protoplasm or cytoplasm. Into this 

 cytoplasm the nourishment of the cell passes. Of 

 bacteria, either in their natural condition or stained 

 for examination, only the nucleus and the wall can 

 be seen, the intervening layer being exceedingly thin. 



FIG. 2 



o 

 a 



OD 



a, staphylococci; b, streptococci; c, diplococci; <7, tetrads; e, sarcinse. 

 (Abbott.) 



In shape, bacteria are either spherical, called cocci 

 (sing., coccus), or straight rods, called bacilli (sing., 

 bacillus), or curved rods, called spirilla (sing., spiril- 

 lum). Each shape has slight variations, such as the 

 flattening of the sides when two organisms are apposed. 

 The spirilla are, perhaps, subject to more variations 



1 See frontispiece for an example of cell. Nearly all living calls are com 

 parable to these leukocytes. 



