is a common saying that "you can't have measles twice". The changes 

 which make one immune during mumps, whooping cough, scarlet fever, 

 yellow fever and diphtheria are practically permanent. 



In former times, people in Asia and in southeastern Europe took advan- 

 tage of the fact that recovering from smallpox usually meant a degree of 

 immunity. They would induce the disease in a mild form by inoculating a 

 person with pus from a patient having the disease. After recovering from 

 the induced smallpox one was just as immune as if he had "caught" it 

 unintentionally. Instead of taking a chance with an epidemic, one could 

 choose to have the disease in a comparatively mild form and perhaps at a 

 convenient time. 



The practice of inoculating against smallpox had long been common in 

 the East. It was not brought to the attention of western Europe and Eng- 

 land until about 1720, through Lady Mary Wortley Montagu, the wife of 

 the British ambassador to Turkey. Inoculation was shown to be relatively 

 safe, as well as effective. Many physicians began to inoculate against small- 

 pox, but the practice met with a great deal of opposition. It was sometimes 

 unsuccessful. Worse still, it sometimes resulted in introducing another dis- 

 ease. In some cases an inoculated person infected somebody else, who then 

 suffered a violent or fatal form of the disease. Inoculation was, at any rate, 

 a strange practice, contrary to familiar customs and to "common sense". 

 George Washington wanted all his soldiers inoculated; later, laws were 

 passed forbidding inoculation. 



For nearly a hundred years controversy raged about inoculation in 

 England, in this country, and in all parts of Europe. Then an English 

 physician, Edward Jenner (1749-1823), was told by a dairymaid that there 

 was no use inoculating her, for she could not have smallpox — she had once 

 had "cowpox". To a learned physician, this was merely ignorant folklore. 

 But to a scientific physician, it was something to look into. Jenner found 

 that this idea was quite general among dairymen and dairywomen, and that 

 they could cite any number of cases. Moreover, dairy people actually had 

 less than their proportion of smallpox. Since cowpox is a very mild disease, 

 Jenner saw advantages in using cowpox pus for inoculating — /'/ it would 

 work. He tried it. He inoculated a boy with cowpox. After several weeks 

 he inoculated the same boy with smallpox. This did not "take". He tried 

 it again, with the same negative results. Later he tried the experiment on 

 others. He concluded that a cowpox inoculation protects against a smallpox 

 inoculation. Would it also protect against smallpox "caught" in the usual 

 way? 



Vaccination^ After years of experimenting, Jenner came to the con- 

 clusion that the cause of cowpox is related to the cause of smallpox. He 



iSee No. 2, p. 246. 

 235 



