SPORULATION: GERMINATION OF SPORES 37 



Generally speaking, when nutritional conditions are favorable, the 

 rate of reproduction is influenced by temperature, growth being most 

 rapid when the temperature is optimum for the organism, less rapid 

 when the temperature exceeds or falls below this point. 



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 char- 

 acter 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. Lehmann and 

 Fried 1 have measured the average speed of certain bacteria in fluid 

 media in millimeters per second. They find that of the -cholera vibrio 

 to be 0.03, typhoid bacillus 0.018, B. subtilis 0.01, B. megatherium 

 0.0075. 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 themselves spores which 

 appear apparently under the stimulus of the stress of conditions unfa- 

 vorable for the continued vegetative growth of the organism. Sporula- 

 tion, in other words, appears to be a specialized mechanism for the 



1 Arch. f. Hyg., 1903, xlvi, 314. 



