330 BIOLOGY AND HUMAN LIFE 



4. Other insect-borne diseases 



Bubonic plague 

 Carried by fleas from mammal to mammal (normally from rat 

 to rat; sometimes from rat to man, then from man to man; 

 sometimes from rat to ground squirrel, then to man etc.) 

 Typhus fever (trench fever) 



Carried by body louse from mammal (man) host to next 

 mammal host 

 Sleeping sickness 



Carried by tsetse fly from mammal to mammal 



5. Measuring importance of insects in relation to disease 



Relation between prevalence of flies and prevalence of typhoid 



and other intestinal diseases 

 Relation between extermination of mosquitoes and elimination 



of malaria ; of yellow fever 

 Relation between rat-flea control and plague control 

 Effects of extermination of insects upon human welfare 



QUESTIONS 



1. What is there to show that flies are dangerous neighbors ? 



2. At what stage in its life history is the fly most easily exter- 

 minated ? Why ? 



3. What can the individual do for his protection if the community 

 continues to tolerate flies ? 



4. What is there to show that mosquitoes are dangerous ? How can 

 we distinguish between mosquitoes that are dangerous and those that 

 are merely a nuisance ? 



5. At what point in the life of the mosquito is it most easily exter- 

 minated ? Why ? 



6. What is there to show that complete extermination of mosquitoes 

 is a possibility? 



7. What is there to show that extermination of mosquitoes elimi- 

 nates disease ? 



8. What is there to show that malaria and yellow fever are not car- 

 ried in the same way as typhoid fever ? 



9. Which is more economical, prevention or cure of malaria ? Why ? 



10. How can a knowledge of the life history and habits of other ani- 

 mals be of use to mankind ? 



