16 THE GENERAL CHARACTERS OF MICROORGANISMS 
upon as possessing a wonderful possibility of reproduction, a force 
of inconceivable magnitude, held more or less in check by adverse 
conditions, but ever ready to exert their influence when the condi- 
tions are favorable. Since they are feeding during their growth, 
they must produce profound changes in the material upon which 
they feed. It is this reserve force, possessed in greater or less 
degree by all bacteria, which makes them such wonderful and 
powerful agents in producing the great changes in nature which 
we are now forced to attribute to them. 
Production of Spores.—New individuals are also produced by 
means of spores. Spore-production has already been mentioned, 
but a further understanding of it is necessary. It is illustrated 
in Fig. rr, a~e. The bacterium there figured consists of a rod. 
The contents of one of the rods collects itself in the center as a 
spherical or oval body, which looks like a hole in Fig. 11, c, because 
the dye used to stain the rod does not 
color the central body. This later breaks 
<— out of the rod, the rest of the individual 
U\p, WZ oe then dying and disappearing. The oval 
Le A) Me body itself is a spore, and is capable, 
° WW when placed under proper conditions, of 
va developing into a new rod, e. Inasmuch 
Big 11 —Sporeformation, * only a single spore arises from a 
a to e, stages m spore for- Single bacterlum, it is not a multiplica- 
mation and germination. ‘tion. Its purpose is not to increase the 
number of individuals but to enable the bacteria to endure 
adverse conditions without being killed. The ordinary bac- 
terla are likely to be killed by being dried, and will readily suc- 
cumb to moderate heat, a temperature of 165°F.* being suffi- 
cient to kill almost any of them. But these spores are covered 
with a hard case which enables them to resist the conditions which 
the active, growing, and multiplying forms cannot resist. They 
may be completely dried for months, and even years, and still 
* Temperatures used in this book always refer to the Fahrenheit scale. 
2 PP Pe 
