474 MAN CONTROLS HIS ENVIRONMENT FOR HEALTH 



Self-Testing Exercise 

 Check the correct statements for your workbook : 



T. F. 1. The incubation period of a disease is the period between 

 the time the germs causing the disease enter the body and the symp- 

 toms of the disease appear. 



T. F. 2. All communicable diseases have the same length incuba- 

 tion period. 



T. F. 3. Children who have been exposed to a catching disease 

 should remain at home during the incubation period. 



T. F. 4. Communicable diseases do not become epidemic. 



T. F. 5. Quarantine means the isolation of a person who has a 

 communicable disease. 



T. F. 6. The length of quarantine differs with different diseases. 



T. F. 7. Epidemics cannot be prevented. 



T. F. 8. We only catch a disease from people suffering from that 

 disease. 



PROBLEM V. WHAT IS IMMUNITY? 



The meaning of immunity. It is a matter of common knowl- 

 edge that some persons in a family will have a very light attack of 

 a communicable disease, while others may have it severely. Some 

 one else may be exposed again and again to this same disease and 

 not take it, because he is immune to, or able to resist, that particu- 

 lar disease, while those who take it are susceptible to its attack. 

 Immunity against disease may be individual, or it may be racial. 

 Negroes, for example, are very susceptible to measles and tuber- 

 culosis, but are less susceptible than white people to malaria, yel- 

 low fever, and smallpox. There are also great differences as to 

 the degree of immunity from the same disease in different species 

 of animals. Tuberculosis of the bovine type may occur in chil- 

 dren as well as in cattle, hogs, and horses. The human tubercu- 

 losis germ attacks only guinea pigs, monkeys, and man. Smallpox 

 and cowpox are probably caused by different types of the same 

 organism. Plague attacks rats, ground squirrels, mice, and guinea 

 pigs, as well as man. A long series of laboratory tests show that 

 most germs that cause illness in man develop ordinarily in man 



