PROBLEM 4. Hoiv We Attempt to Stop the Spread of Disease 345 



Fig. 305 Each curve shows 

 the death rate fro?/! typhoid 

 per 100,000 people in Al- 

 bany, New York, during 

 each fuonth of the year. The 

 upper curve shows the num- 

 ber before the drinkiitg wa- 

 ter was filtered; the lower, 

 after filtration. What was 

 the highest rate before filtra- 

 tion? What was the highest 

 rate after filtration? What 

 besides filtration helps in 

 conquering typhoid? (saun- 



DERS) 



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by treating it with chemicals. Second, 

 the community must safeguard its drink- 

 ing water. Water free from all pollution 

 is difficult for a city to obtain. Some 

 cities, such as New York, Boston, and 

 Los Angeles, construct huge reservoirs 

 many miles away. The water in the 

 streams and lakes of the watershed (the 

 region supplying the reservoir) is 

 guarded against pollution. Before it en- 

 ters the large pipes that carry it to the 

 city, it is aerated (mixed with air), and 

 otherwise cleaned. Other cities follow a 

 different practice. They collect the 

 available water, even if possibly polluted, 

 and then purify it by passing it through 

 huge sand filters and treating it with 

 chemicals, like chlorine, which kill the 

 microorganisms. Partly because of meas- 

 ures such as these and partly also because 

 of widespread immunization, typhoid 

 fever has become rare in the United 

 States and most of Europe. Study Figure 

 305 to see what effect filtration of water 

 had on the number of typhoid cases in 



Albany, New York, years ago. Try 

 Exercises 2 and 3. 



Safeguarding the milk supply. In the 

 milking of cows and the later handling 

 of milk, a person who has germs in his 

 body may transfer them to the milk. The 

 bacteria may live and reproduce there. 

 Serious epidemics of septic sore throat 

 and other diseases have been started in 

 this way. Then, too, if the cow has tu- 

 berculosis, undulant fever, or another of 

 the diseases which attack both man and 

 cattle, these germs may be in the milk. 

 For this reason, at one time people drank 

 boiled milk. But it was found that boil- 

 ing changes the taste of milk and makes 

 it unsuitable for babies. The problem 

 was solved by the pasteurization of all 

 milk sold to the public. It is required in 

 most communities. The process was 

 named in Pasteur's honor since he treated 

 wines and beer in a similar way to keep 

 them from spoiling. When milk is pas- 

 teurized, it is first heated to a tempera- 

 ture of about 150° F for about half an 



