270 HOW WE FIGHT BACTERIAL DISEASES 



so abundant in the body that the}^ give off sufficient toxins to 

 cause the symptoms of the disease. This period, between the time 

 when the germs enter the body and the time the symptoms of 

 disease appear, is called the incubation period. Since this period 



James 

 left school 

 Oct 15th, ill. 

 No physicidP 



wdscdlled 



John 



^sdt with Jams' 



[Developed measles' 



}loY.lst.()udrdfitine(lj 



NoY.M 



Junior 



^pldyedmfh John 



finscliool.DeYeloped 



measles MM. 



^QuaranhnedNoY.^ 



2n£ 



The failure to recognize James's illness as measles resulted in its spread to three 

 other cases. Strict quarantine prevented its further spread. 



varies for different diseases, the period of quarantine also varies, 

 as seven days for scarlet fever, fourteen days for whooping cough, 

 twenty-one days for chicken pox. 



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 that particular disease, while 

 those who take it are susceptible to its attack. Immunity against 

 disease may be individual, or it may be racial. The Negro race, 

 for example, is very susceptible to measles and tuberculosis and in 

 a lesser degree to yellow fever. White people are much more sus- 

 ceptible to malaria, yellow fever, and smallpox. There are also 

 great differences as to immunity from the same germ in different 

 species of animals. Tuberculosis of the bovine type may occur in 

 children as well as in cattle, hogs, and horses. The human tuber- 



