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Our Surroundings 



named because of their resemblance to minute rods. As they grow 

 they break in two, or lengthen into long slender threads which 

 finally break up into rods. Some have tiny organs of motion and 

 are very active. The third type is spiral. It should always be 

 kept in mind that all forms of bacteria are so tiny that they can 

 be observed only by the aid of high powers of the microscope. 



BACTERIA THE SMALLEST KNOWN PLANTS 



A Spherical. 

 B Rod-shaped. 

 C Spiral. 



Bacteria may be placed in two classes : first, those that live on 

 decaying matter; second, those that get their food from higher 

 living organisms. The first class are known as saprophytes, the 

 second class are known as parasites. The latter include the disease- 

 producing bacteria. 



Life History. As in the case of all other living things, 

 food, moisture, oxygen and some degree of heat are necessary 

 for the growth and development of bacteria. They respond 

 most favorably to a temperature about that of our own bod- 

 ies, and to a location not exposed to direct sunlight or fresh 

 air. If exposed to bright sunlight they perish rapidly. When 

 conditions are right, each bacterium grows to full size, and 

 immediately divides into two equal parts, thus producing two 

 individuals. 



When conditions for life are unfavorable, some bacteria are 

 able to continue their existence by developing a thicker cell cov- 

 ering which protects them. While in this form they are called 

 spores. Although they seem lifeless, with the reappearance of 

 favorable conditions, especially of heat and moisture, they 



