SMALL-POX AND VACCINIA 259 



vaccination. The disease so inoculated runs a mild course, 

 and it has been conclusively shown that an individual who 

 has had vaccinia is protected against small-pox just as if he 

 had had that disease. 



In the East it has been, time out of mind, the practice 

 among the natives to take a flake of skin of a small-pox 

 patient and use it for inoculating others with the disease, 

 as it was well known that small-pox thus produced runs a 

 milder course than if it is acquired by natural means. It 

 was also well known that an attack of small-pox protected 

 against a second infection. This practice was introduced 

 into Europe from the East about the time of the Crusades, 

 and up to the end of the eighteenth century was the only 

 means employed to alleviate the terrible ravages of this 

 disease, which formerly used to ravage all the countries of 

 Europe. The great disadvantage of this method was, 

 however, that the resulting attack of small-pox, though 

 mild, was very infectious. 



In 1798 Jenner published his paper entitled, 'An Inquiry 

 into the Causes and Effects of the Variola Vaccinae,' which 

 contained the results of his remarkable observations and 

 inquiries respecting small-pox and cow-pox. Jenner found 

 that individuals who had contracted cow-pox from affected 

 cows, or a similar disease of horses known as ' grease ' or 

 horse-pox, were remarkably insusceptible to small-pox. 

 Jenner produced experimental evidence to show that 

 persons who had suffered from cow-pox did not react to 

 small-pox when inoculated, and further, that persons who 

 had been artificially inoculated with vaccinia were also 

 immune to small-pox. 



At first Jenner's views met with the greatest opposition ; 

 but when the first prejudice was overcome, the operation 

 soon became very popular. 

 Although vaccination does not confer absolute immunity, 



17—2 



