GENERAL BACTERIOLOGY 
29 
placed in suitable surroundings the spores germinate and 
the original bacteria reappear. The spore formation is 
most frequent among those bacteria which live without 
air (anaerobes), and special staining methods are required 
for the demonstration of spores. 
III. Bacterial Reproduction 
The bacteria being minute unicellular asexual cells, the 
reproduction is a simple mechanical process, the cell hav¬ 
ing reached its maximum size (which is fairly constant 
for the species) a slight constriction appears, which deep¬ 
ens until a distinct partition or septum is formed, and 
the original cell is split into two cells, each being a com¬ 
plete organism, identical with the parent cell. Some of 
the higher bacteria (e. g., Spirocheta pallida, which 
causes syphilis) split not transversely but longitudinally 
(Noguchi). The rate of growth, that is the time elapsing 
between two successive cleavages, is about 15 to 20 minutes 
(Fischer), so that a single colon bacillus would yield about 
1,500 trillion in a single day. 
IV. Constancy and Mutation of Type 
While most of the bacterial properties remain constant, 
especially the disease-producing (pathogenic, from Greek 
pathos , meaning disease, and geneo, meaning to produce) 
properties, the beginner must remember that under certain 
conditions one or more characteristics of a given species 
of the bacterium may be lost, such variation has already 
been referred to in the connection with the capsule forma¬ 
tion. Pasteur succeeded in producing sporeless anthrax 
bacilli by growing them at 43° C. (instead of 37° C. 
which is the temperature at which they grow best nor¬ 
mally). 
The experience accumulated so far seems to point to 
