EXCRETION AND SEWAGE 255 



REVIEW TOPICS 



1. Explain the difference between a secretion and an 



excretion. 



2. Name the principal excretions and tell how they leave 



the body. 



3. Describe sweat glands and the perspiration as an 



excretion. 



4. Describe the kidneys and their excretion. 



5. Discuss how imperfect oxidation may overwork the 



kidneys. 



6. Show how the skin aids the action of the kidneys and 



how the one acts less when the other is more active. 



7. Show how alcohol produces kidney diseases and how 



sugar acts in the same way. 



8. Describe three ways in which nature destroys the 



excretions of man. 



9. Discuss the dangers which may arise from sewage. 



10. Tell how sewage is disposed of in cities. 



11. Describe how sewer gas is prevented from entering 



houses through waste pipes. 



