Fig. 3.—Spirilla of Various Forms. (Williams.)
Fig. 4.—Bacteria showing Flagella. (Williams.)
Under favorable conditions fission occurs rapidly; in some types a new generation may appear as often as every 15 minutes. Enormous
multiplication would result if nothing occurred to check the process. But in nature such increase never continues unhindered, and bacteria, acting upon their food substances, produce acids and other materials injurious to themselves. Furthermore, lack of proper food, moisture, or favorable temperature, and competition with other organisms tend to prevent their unrestricted growth and multiplication.
Fig. 5.—Bacteria with Spores. (Williams.)
Spores.
—Most bacteria die if conditions become unfavorable to their growth, but some enter into a resting stage. This stage is characterized by the development of round or oval glistening bodies called spores, which are of dense structure and possess an extraordinary power to withstand heat, chemicals, and unfavorable surroundings. Except in rare instances a single cell produces but one spore. As soon as favorable conditions of temperature, moisture, and food supply are restored, the spore develops into the active form of the germ; it may, however, remain dormant
for months or years. Spore formation, however, occurs in only a very few varieties of pathogenic bacteria.