516 
PREVENTION OF DISEASE 
The second important measure to be adopted to prevent 
an epidemic after the communicable disease has appeared is 
the prompt quarantine of the first cases and immediately 
putting into operation the regulations of the Board of Health 
for communicable diseases. 
398. Heredity of Disease. — The term heredity of disease 
is one which has been misunderstood by many people. By 
the term heredity we mean that which is handed on from 
parents to their offspring. In the case of biological diseases 
which are caused by some definite plant or animal, it is 
evident that they cannot be inherited. But when the 
parents are afflicted with a biological disease, their bodies 
become weakened 'and their offspring may have a poor 
constitution so that they are more easily affected by disease. 
397. Immunity. — Immunity is a technical term which 
means that the body resists or is not susceptible to the 
germs of biological diseases. Many persons do not become 
sick when there is an epidemic of typhoid fever, measles, 
malaria, or the like. Such persons are said to possess a high 
degree of natural immunity to disease germs. People 
usually well frequently take germ diseases when the body 
happens to be exhausted by care or work. In such cases 
the immunity of the body has been weakened. Many of 
the germ diseases confer immunity against a second attack 
of the same disease, but this does not hold true for all per¬ 
sons or for all germ diseases. Vaccination against smallpox, 
in the case of most persons, confers immunity for about seven 
years. Inoculation with the typhoid serum confers im¬ 
munity for from two to three years. Immunity, then, is a 
relative term, and depends in a large measure on the state 
of health of the individual and on his power of resisting the 
poisonous effects of disease germs. 
Some idea of loss of immunity is gained from a study of 
the increase in tuberculosis by Homer Folks, War, Best 
Friend of Disease, in Harper’s, March, 1920. 
