510 
PREVENTION OF DISEASE 
wrote in 1754 that every tenth death was due to smallpox, 
and that one fourth of mankind was either killed by it or 
disfigured for life. Smallpox was brought into the Western 
Hemisphere soon after the discovery of America and killed 
thousands of the Indians. It also affected the colonists. 
In 1721, Boston was ravaged for the sixth time by this 
disease. Out of the 10,567 inhabitants, 5989 had the 
disease and 894 died. 
In 1796, Jenner, an Englishman, demonstrated the fact 
that by inoculation of a person with cowpox, a disease 
peculiar to cows and in some way allied to smallpox, the 
patient would become immune to the dreaded disease. 
This was one of the greatest and most beneficial discoveries 
of medicine which has ever been made. 
As the result of vaccination and sanitation smallpox has 
become a rare disease in the civilized nations of the world, 
and is least prevalent where the vaccination laws are the 
most stringent. 
Vaccination for smallpox consists in the inoculation of 
the human patient with vaccine, a substance secured from 
a cow suffering from cowpox. This usually causes a slight 
illness, but during the illness the patient acquires a power 
which enables him to resist the germs of smallpox. This 
acquired power of resistance is called immunity. Im¬ 
munity secured through vaccination or through having a 
disease, such as whooping cough for example, is described 
as acquired immunity to distinguish it from that form of im¬ 
munity to all diseases or to certain diseases which many 
people possess. This latter is natural immunity. Those in 
the class who have not had measles may be said to have a 
natural immunity against measles. Those in the class who 
have had measles once have an acquired immunity against 
measles. 
Many people do not understand the theory of vaccina¬ 
tion and its advantages, and have opposed its use through 
