Vaccination 93 



By both methods the very disease, variola, against which protec- 

 tion was desired, was induced, the only advantage of the experi- 

 mental over the accidental infection being that by selecting the 

 infective virus from a mild case of variola, by performing the 

 operation at a time when no epidemic of the disease was raging, 

 and by doing it at a time when the person infected was in the most 

 perfect physical condition, the dangers of the malady might be 

 mitigated. 



There was always danger, however, that the induced disease being 

 true variola might prove unexpectedly severe, or even fatal, and 

 that each inoculated individual, suffering from the contagious dis- 

 ease, might start an epidemic. 



2. Jennerian vaccination: In 1791 a country schoolmaster named 

 Plett, living in the town of Starkendorf near Kiel in Germany, 

 seems to have made the first endeavor to subject the oft-repeated 

 observation, that persons who had acquired cow-pox did not subse- 

 quently become infected with smallpox, to experimental demon- 

 stration, by inserting cow-pox virus into three children, all of whom 

 escaped smallpox. 



The father of vaccination, and the man to whom the world owes 

 one of its greatest debts, was Edward Jenner, who performed his 

 first experiment on May 14, 1796, when he transferred some of the 

 contents of a cow-pox pustule on the arm of a milkmaid named 

 Sarah Nelmess to the arm of a boy named John Phips. After the 

 lad had recovered from the experimental cow-pox thus produced, 

 he subsequently introduced smallpox pus into his arm and found 

 him fully immunized and insusceptible to the disease. This led 

 Jenner to perform many other experiments, and record his ob- 

 servations in numerous scientific memoirs. The success of his 

 work immediately attracted the attention of both scientific investi- 

 gators and sanitarians, and its outcome has been the establishment 

 of compulsory vaccination by legal enactment in nearly all civilized 

 countries, with the result that smallpox, instead of being one of the 

 most prevalent and most dreaded diseases, has become one of the 

 most rare and least feared. 



The immunity acquired through vaccination is active and usually 

 of prolonged duration. It is subject to the same variations ob- 

 served in other experimentally acquired immunities, these varia- 

 tions explaining the occasional failures which constitute the " stock 

 in trade" of those who still remain unconvinced of the scientific 

 basis and efficacy of the procedure. 



Though a thorough analysis of the irregularities and exceptions 

 of vaccination would be of much interest, a brief mention of the 

 most important must suffice for the present argument. 



The first controversial point is the nature of the " vaccine," or 

 yirus used in the operation. It is obtained from calves or heifers 

 suffering from experimental cow-pox, and is a virus descended from 



