REVIEW QUESTIONS 135 



opment of a disease which is caused by bacteria is due 

 to their growth within the body. If the body is in a 

 good condition the bacteria will be overcome by forces 

 within the body; it is usually a weak body which is easily 

 attacked by bacteria. Thus the best way to prevent 

 being sick is to take good care of the body. This means 

 eating the proper food, sleeping enough and not doing 

 anything which is harmful to the body. It means bodily 

 cleanliness and clean houses. It means good ventilation, 

 plenty of sunlight, and breathing fresh air both day and 

 night. 



Cleanliness, if complete, is the greatest help to sani- 

 tation. Sanitation means freedom from harmful bacteria. 

 Review Questions, 24. 



1. What Use is made of nitrogen? 



2. Name all the sources of carbon dioxide we have 

 studied. 



3. What 5s the use of carbon dioxide? 



4. What are the needs of all living things? 



5. What is yeast? What can yeast do? 



6. What are bacteria? Are all bacteria harmful? 



7. How can you keep milk from souring? Which 

 is the worst way and which is the best way? 



8 Whv should we clean our teeth at night when no 

 <onc is to see them? 



9. Why should we keep clean? 



10. What is the best way to prevent being sick? 



Next year we shall study more about plants and 

 animals. Now we are going to learn about what plants 

 and ani^mls need for food and about the food which 

 thev make. 



