Vaccination 99 



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 disease, 

 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 demonstra- 

 tion, 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 fuUy immunized and insusceptible to the disease. This led 

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

 tions in numerous scientific memoirs. The success of his work 

 immediately attracted the attention of both scientific investigators 

 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 observed 

 in other experimentally acquired immunities, these variations ex- 

 plaining the occasional failures which constitute the "stock in 

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

 and efl&cacy 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 

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

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

 various spontaneous cases of cow-pox observed in places remote 

 from one another. Experts are undecided whether cow-pox is 

 variola modified by passage through the cow so that the trans- 

 planted micro-organisms are only capable of inducing a local 

 instead of general disease, or whether it is an independent affection 

 natural to the cow. 



