426 SANITATION 



to cause a given disease; no other germ will ' ' do just as well." But the 

 ways of different kinds of germs are not at all alike; it is often very hard 

 for the investigator to know just how each kind of germ gets into the 

 body, and how it does its work. Thus, it turns out that while a cer- 

 tain mosquito, called anopheles (a-nof'-e-les) , carries malaria germs 

 from one person to another, only -the female anopheles sucks blood, and 

 is responsible for the spreading of malaria. 



The science of germs, and of the way in which we can 

 deal with them, is bacteriology. The science of keeping 

 the body in good health is hygiene. The study of the 

 conditions and surroundings that make for the health of 

 the body and of the community, is sanitation. 



422. How the Body Gets and Resists Diseases. 

 Germs, like other living organisms, grow rapidly when the 

 conditions for life (environment; cf. 306) are favorable. 

 They need animal or vegetable material for food; they 

 need moisture; they need a favorable temperature. 

 Germs often find these conditions in our solid food, in 

 milk, in water containing organic matter, in the filth of 

 the streets, and in the animals that make their home 

 with man. These animal companions of man are ver- 

 min, pets, and domestic animals. From food, and 

 water, and animals, then, disease germs are transferred 

 to man. In the body of man they find conditions favor- 

 able, and thrive enormously. The stomach secretion 

 kills many, but certain kinds are able to get through the 

 stomach (cf. 364). Some find favorable conditions in 

 the warm, moist cells of the throat and lungs; others, 

 still, get into the blood through cuts and scratches in the 

 skin. When we think of how constantly we come in con- 



