160 GERM DANGERS AND HEALTH HABITS 



dish, yet each bacterium is so small that it is visible only 

 under a very high power microscope. Bacteria are single- 

 celled plants, unable to make their own food, and con- 



Types of bacteria, i. Rods. 2. Spheres. 3. Spirals. 



sequently do much harm by living at the expense of 

 other things, as upon dead organic material. Some one has 

 said that in order to recall their forms one must think of 

 a billiard cue, a billiard ball, and a corkscrew. A glance 

 at the illustration will show how true this statement is. 

 They are rodlike (called bacillus), ball-like (called coccus), 

 or spiral (named spirillum) in form. Many kinds can 

 move with great speed through the water by means of 

 tiny threadlike structures which vibrate rapidly. They 

 never thrive except in moisture, although 

 some of them may be dried and float 

 around in the air some time without dy- 

 ing, becoming active again when moist. 

 Many forms endure an unfavorable en- 

 vironment of heat and cold as well as 

 dryness by forming a thick resistant 

 coat about their body. In this condi- 

 tion they are called spores. 



How germs cause disease. It has been estimated 

 that over fifty per cent of the people who die each year are 



Bacteria forming spores. 



