30 THE MORPHOLOGY OF BACTERIA 
typhoid bacillus they are distributed around the sides of the organism 
but do not occur at the ends. IVIany of the Spiroch<Teta and Trepone- 
mata are impelled through fluid media by rhythmic contractions of 
their bodies. 
Spores. — £??r/o5pore5.^— Many bacteria die when their environment 
becomes unsuited for further growth. Death may result from the 
presence of inimical substances, the absence of essential foods, or the 
intervention of unsuitable physical conditions. Death is manifested 
by a cessation of chemical interchange between the bacterial cell and 
its environment. There is a group of bacteria, however, usually of 
saprophytic origin, which is able to survive even prolonged exposure 
to unfavorable en^'ironmental conditions by passing into a latent stage 
during which chemical interchange with the environment is at an 
extremely low ebb. This latent stage or hibernation has been known 
to last for more than two decades in certain instances, and yet the 
organisms have resumed their original luxuriant growth when placed 
under favorable environmental conditions. The bacteria which exhibit 
this latent state produce within their substance highly refractile, spher- 
(S> 
V 
^ff % ^/ 
Fig. 3. — Types of bacterial spores. 
ical or o\al bodies called spores. Spores are not found in \'ery young, 
actively growing cultures, as a rule. Spore formation is ushered in 
by a clouding of the endoplasm of the bacterial cell, which gradually 
becomes granular. The granules coalesce, eventually appearing as 
the mature spore which is surrounded by a dense membrane, fre- 
cjuently exhibiting a double contour when stained by dilute carliol 
fuchsin.2 The spore membrane (ectoplasm) is relatively impermeable 
to heat and disinfectants. This confers the resistance to physical 
agents which spores exliibit upon exposure to such influences. But one 
spore is formed in an individual bacterium, except under most unusual 
conditions. It is to be emphasized, consequently, that spore formation 
is not a reproductive process. The mature spore may form in the 
center of the bacterium, at, or near one end. The spore may be 
roimd or oval, and greater or lesser in diameter than the parent cell. 
If the spore is greater in diameter it distends the cell membrane, 
producing a spindle-shaped organism if the spore is in the center of 
the rod: if the spore is at one end, a drumstick-shaped organism results. 
1 Endospores were probably first seen by Perty (Zur Kenntnis kleinster Lebensformen, 
1852). They were described in detail by Cohn (Beitrjige zur Biologie der Pflanzen, 1872, 
No. 2, 1, 145, 176; 1876, No. 2, Heft 2. 
2 Meyer, A. : Practicum der botanischen Bakterienkunde, Jena, 1903. 
