318 GENERAL SCIENCE 



4. Why may scarlet fever always be considered a serious disease? 



5. Why will tetanus (lock jaw) germs die if exposed to sunlight 

 and air? 



6. What are some of the sources of tetanus germs? 



7. Why are people sometimes seriously ill from ptomaine poison- 

 ing after eating canned food? 



8. Why should a wound under a finger nail be carefully attended to? 



9. What are the chief sources of blood poisoning? 



10. What is the value of determining the opsonic index of a 

 person? 



11. Why does pus form in some cases of inflammation? 



12. Why is the hookworm a detriment to civilization? 



13. What diseases of trees caused by bacteria should one be 

 careful to look for? 



14. How can you tell by the appearance of a potato whether it is 

 diseased or not? 



15. Find a potato infected with potato scab. 



16. Why should children be kept home from school if a child in 

 the family has measles? 



BACTERIA USEFUL TO MAN 



Useful Bacteria. We have studied a great deal about harmful 

 bacteria. There are many more bacteria which are useful to man 

 and animals. 



Bacteria in the Soil. Plants require a large amount of nitrogen 

 in simple compounds of nitrates and nitrites. Much of the fertilizer 

 which is put into soil contains large quantities of nitrogen in com- 

 pounds which are not available for the roots of the plants. Large 

 numbers of bacteria in the soil attack this material, and change it 

 into compounds which are useful food for the plants. Sometimes 

 the soil has so few bacteria in it that farmers plant certain types 

 of vegetables on which other bacteria live. On such plants as clover, 

 cowpeas, vetches, alfalfa, the bacteria form knotty growths called 

 tubercles. Through the activity of such bacteria, large quantities 

 of nitrogen are taken from the air to enrich the soil. Encouraging 

 the growth of such bacteria obviates the necessity of buying large 

 quantities of expensive fertilizers. 



