312 BIOLOGY AND HUMAN LIFE 



In a general way all these methods are used. Discharges from 

 sick people are sterilized (that is, poisoned so as to kill the 

 bacteria) or burned; utensils and clothing are sterilized by 

 fumigation or otherwise, or burned ; and entry of bacteria is 

 prevented. That these methods are actually effective is indi- 

 cated by the steady decline in the prevalence of various com- 

 municable diseases (see Fig. 147). 



240. Individual protection. The most general means of pre- 

 venting infection is through the protection of our food and drink 

 from contamination. This means that we must take pains to 

 protect fresh food from dust, from the mouth spray or nose 

 spray of people or other animals, and from contact with unclean 

 hands, containers, or other objects. Each of us can at least clean 

 his own hands before every meal, avoid the use of cups and 

 towels that have been used by others since the last cleaning, 

 sterilize a cut or wound (see page 188) on his own skin, and 

 avoid food that has been unduly exposed. On the other hand, 

 we can avoid endangering others by refraining from spitting 

 where the bacteria in the spit will have a chance to be scattered ; 

 we can cough or sneeze into our own handkerchiefs instead of 

 into the air ; we can keep our hands off food or other objects 

 that are to be used by other people. But we shall find that, no 

 matter how particular v/e are about protecting our own skins, 

 so to speak, we shall always be exposed to the ignorance or 

 carelessness of other people, and no matter how thoughtful or 

 considerate we are individually, there are many details that we 

 simply cannot look after ourselves. For these reasons it be- 

 comes necessary to establish sound methods of carrying on the 

 routine work of certain classes of people, as well as to establish 

 regulations for all of us. Finally, it is necessary for special 

 work to be done by people who are especially appointed for 

 it, because it is impossible for each individual to do his part. 

 This is true, for example, in protecting a city's water supply 

 or in exterminating the mosquitoes of a region (see Chap- 

 ters XXXIV, XXXVI, etc.). 



