136 BACTERIOLOGY. 
as moisture is present, however, their activilies are resumed. They 
may have retained life in their original form or in the form of spores, 
of which more will be said later on. 
What is the structure of a bacterium ? 
It is a single cell, either spherical or rod shaped, and is composed of 
an albuminous material surrounded by a gelatinous wall or capsule. 
It has not been definitely determined whether or not it contains a 
nucleus. The capsule may under certain conditions swell vp and cause 
different individual organisms to stick together, thus forming either 
a pellicle or thread-like masses. 
How do bacteria develop? 
From pre-existing cells of the same character and never ‘sponta- 
neously. 
CLASSIFICATION, MOVEMENT AND GROWTH 
OF BACTERIA. 
How are bacteria classified ? 
By their shape. 
Name the three great divisions or classes of bacteria. 
Micrococct or spherical-shaped forms. 
Bacilli or rod-shaped forms. 
Spirilli or corkscrew-shaped forms. 
Into what classes are the micrococci subdivided ? 
Staphylococci, growing in irregular masses. 
Streptococct, growing in chains like a string of beads. 
Diplococci, growing in pairs. 
Sarcinz, growing in fours or multiples of fours. 
What are some of the peculiarities of bacilli as regards arrange- 
ment and appearance ? 
Some are long and slender, others are short and thick and may even 
resemble micrococci. In growing they may develop in irregular masses 
or in long threads or chains. They may also be slightly curved so that 
when joined together end to end they form a long spiral. 
What may be said of the appearance of the spirilli ? 
They are shaped like a corkscrew and their spirals may be close or 
open and few or many in number. Some members of this class 
have one or more fine filaments or cilia at each end. 
