INFECTIOUS DISEASES 419 



be covered with germs. Dirty water, impure milk, and 

 soiled food also spread the germs. If we observe the mod- 

 ern standard of cleanliness which is set by good society, 

 we shall keep ourselves free from most disease germs. 



Many diseases are spread by the habit of putting things into the 

 mouth unnecessarily. Sucking the ends of the fingers, wetting the 

 fingers with the lips on turning the leaves of a book, and touching 

 the point of a pencil to the tongue on writing are often the means of 

 spreading diseases. 



A grave source of danger is a public drinking cup. It is impossible 

 to take a cup between the lips without leaving saliva on the cup. 

 Germs of tuberculosis have often been found on cups in railroad 

 stations and schools. A public drinking fountain should be so arranged 

 that we may drink directly from a stream of running water without the 

 need of a cup. 



725. The weather and infectious diseases. When the 

 germs of an infectious disease grow in any part of the body, we often 

 say that we have taken cold there, but the expression is an uncertain 

 and indefinite one which came into use at a time when the weather was 

 supposed to cause epidemics and pestilences. Infectious diseases are 

 not caused by cold air, or dampness, or any other condition of the 

 weather, for disease germs are seldom found in the open air. During 

 cold, damp weather people often keep their doors and windows closed 

 tightly, and thus they breathe air which is foul and dusty and full of 

 disease germs. They are likely to have nose and throat troubles, and 

 lung diseases which they catch from the bad air of their houses and 

 not from anything wrong with the outdoor air. We may be as free 

 from colds and lung troubles in winter as in summer if we keep our 

 houses and meeting places as clean and well ventilated in cold weather 

 as in the summer time. 



Hot weather is often supposed to cause intestinal diseases. These 

 forms of sickness are not due to the heat itself, but are usually caused 

 by spoiled food or by house flies. 



726. Suppression of infectious diseases. There are several 

 reasons why it is difficult to suppress infectious diseases entirely : 



i. A person who is just coming down with a disease may give its 

 germs to others before he knows that he has it. Thus measles may be 



