GENERAL BACTERIOLOGY 
25 
thrax bacillus, which is from 5 to 10 /x long. The spiril¬ 
la vary greatly in size. 
The weight of bacteria is, of course, extremely light, 
the average being about 0.000000001 milligram, that is to 
say that sixteen hundred million bacilli weigh approxi¬ 
mately one milligram; a normal red blood cell is fifty 
thousand times as heavy as a single colon bacillus. 
II. The Structure of the Bacterial Cell 
The bacterial cell has an external membrane that is 
rigid and maintains the shape of bacteria and is called 
ectoplasm (from the Greek ecton, meaning without, 
and plasma, meaning a formed thing). 
( t 
Jj 
n 
B C 
Fig. 1 —A, bacilli; B, cocci; C, spirilla. 
The thickness of this cell wall varies, being thicker in 
the old than in the young organisms; special stains are 
required for the demonstration of the ectoplasm. 
The substance which comprises the interior of the bac¬ 
terial cell is called the endoplasm (from Greek endon, 
meaning within), and plasma, or cytoplasm (meaning cell 
substance) ; this is a clear, colorless, highly retractile sub¬ 
stance. Whether or not there is a nucleus (kernel) in the 
bacterial cell is not yet definitely settled, although the 
majority of bacteriologists are inclined to believe there 
is at least a nuclear substance if not a definite nucleus. 
Certain bacteria, notably the diphtheria group, exhibit 
one or more granules which are scattered irregularly in 
