INSECTS, AND THEIR RELATION TO MAN 183 



grow for about one week, then pupate for another week, 

 when they emerge as adults. How long is their life his- 

 tory? 



2. Flies also breed in excrement of any sort. Suppose this 

 excrement should come 



from those suffering from 

 bacterial diseases, and 

 the flies breeding therein 

 should travel directly to 

 foods. What will most 

 surely happen? 



3. Study Figure 50. A 

 fly was allowed to walk 

 over some material (gela- 

 tine) that is food for bac- 

 teria. Each white spot 

 shoys where a germ was 

 left, and a colony has 

 grown from it. Where 

 did the fly probably ob- 

 tain the bacteria? 



Conclusions. 1. What must surely happen if flies are per- 

 mitted to crawl over our food, or on our hands and faces ? 



2. How may typhoid and other diarrheal diseases be spread 

 about ? 



Observation. Refer to Figure 51. 



Conclusions. 1. Write a paragraph concerning the dangers 

 of open spittoons, or of spitting in public places. Remedies ? 



2. Tell of the dangers of any open garbage pails, or toilet 

 closets, or any exposed decomposing vegetable or animal 

 matter. 



3. Why should fruit dealers and others selling food of any 

 description see that their goods are protected from flies and 

 street dust? 



4. Why should the doors and windows of dining rooms and 

 kitchens especially be screened? 



FIG. 50. Bacteria left by fly passing over 

 gelatine plate. (Courtesy of The Mer- 

 chants' Association of New York.) 



