SPORULATION: GERMINATION OF SPORES 37 
B. MOTILITY: RATE OF MOTION. 
The rhythmic contractions of the flagella, with which practically all 
motile bacteria are provided, drive the organisms through fluid media 
in which they may be suspended, some slowly, some rapidly. Not all 
bacteria even in the same culture exhibit motility. The character of 
the motion may be direct, serpentine, oscillatory, or irregular. Rarely, 
the flagella appear to produce local currents in the medium which 
immediately surrounds the organism. Various environmental factors 
incite or inhibit motility. Chemotactic substances may attract 
bacteria, thus in a sense directing their line of movement. Other 
substances, as protoplasmic poisons, paralyze bacterial movements. 
Oxygen appears to increase the motility of aerobic bacteria, and it 
inhibits motility in the anaerobes. Generally speaking, in favorable 
media motility increases with the rise in temperature to the optimum. 
If this temperature is exceeded, even by a very few degrees, motion 
ceases. 
The rate at which bacteria progress through a fluid is a variable 
one, although with a given organism under favorable conditions it 
appears to be fairly constant. It must be remembered that the 
apparent rate of motion observed under the microscope is increased 
proportionately to the increase in magnification. Fried^ has measured 
the average speed of certain bacteria in fluid media in millimeters per 
second. He determined that of the cholera vibrio to be 0.03, typhoid 
bacillus 0.018, B. subtilis 0.01, B. megatherium 0.0073, and B.' tetani 
0.01 mm. If a man traveled at a rate of speed in proportion to his 
size as great as that of the cholera vibrio, he would average more than 
a mile a minute.^ 
C. SPORULATION: GERMINATION OF SPORES. 
Many saprophytic bacteria form within their cytoplasm spores 
which appear apparently under the stimulus of the stress of conditions 
unfavorable for the continued vegetative growth of the organism. 
Sporulation, in other words, appears to be a specialized mechanism 
for the perpetuation of the organism during periods of environmental 
unfitness. Whether spore formation is a definite phase in the life- 
history of spore-forming bacteria is not definitely settled.'' Sporula- 
tion is rarely observed w^hen the temperature of the environment falls 
much below 15° C, although considerable latitude is observed among 
the spore-forming bacteria in this respect. Among anaerobic bacteria, 
particularly those that ferment sugars intensely, sporulation usually 
takes place only in media free from utilizable carbohydrates. It seems 
1 Inaug. Diss. Wurzburg, 1903. Review: Centralbl. f. Bakteriol., ref., 1903-1904, 
34, 775. 
- Gabritschewsky: Ztschr. f. Hyg., 1900, 35, 104. 
3 Literature by Miihlschlegel : Centralbl. f. Bakteriol., II abt., 1900, 6, 106. 
