

PREVENTIVE INOCULATION. 121 



lost their virulence, while those forgotten in the open bottle in the 

 incubator and exposed to the access of air had done so. Oxidation 

 proved indeed to be one of the most general methods of artificially pro- 

 ducing attenuated virus, to which method later on were added others — 

 the effect of light, of chemicals, of passage through certain animals, etc. 



And, of course, the last and crowning conclusion was that an ordi- 

 nary, susceptible fowl that has undergone the injection with an at- 

 tenuated culture becomes immune against a culture which kills other 

 fowls; and that conclusion, in the particular circumstances under which 

 Pasteur was working, proved to be true. 



Pursuing the new line of research, Pasteur demonstrated that a 

 protection similar to that obtained against smallpox and chicken cholera 

 could be secured also against anthrax, a disease which, by the destruc- 

 tion it caused among sheep and cattle, was entailing heavy loss on the 

 farmers of France. After a long series of experiments he prepared 

 two specimens of virus, different in strength, but both weaker than the 

 natural contagion, and worked out the proportions in which sheep, 

 horses and cows could be safely injected first with the weakest virus and 

 then with the virus of the somewhat greater strength, after which 

 they became capable of withstanding the strongest anthrax infection. 



In honor of Jenner, who was the first to discover the way of pre- 

 paring a virus of a fixed strength safe to be used for the preventive 

 treatment of men, Pasteur proposed that all such artificially bred, so 

 to say, domesticated forms of microbes be called vaccines, while the 

 word virus be reserved for a contagion growing in nature in a natural 

 condition, or taken direct from an infected individual. The French 

 distinguish between 'vaccin,' which is used as a generic term in 

 Pasteur's sense, and 'vaccine,' which name they reserve for smallpox 

 vaccinia lymph. The word 'vaccination' has been also extended to desig- 

 nate inoculation with artificially vaccinized virus, while the word 'inoc- 

 ulation' is used for the injection of a natural, not vaccinated virus, 

 taken direct from a patient. The latter distinction is, however, not 

 yet strictly maintained in English literature, nor in the subsequent 

 pages of this paper. 



Pasteur gave a memorable demonstration of the efficiency of his 

 method of anthrax vaccination. At Pouilly-le-Fort, in the midst 

 of an assemblage of scientists, delegates of agricultural societies, gov- 

 ernment officials, landlords, farmers and representatives of the press, 

 he performed the following experiment: Sixty sheep were taken; ten of 

 these were put aside, twenty-five were vaccinated with the two atten- 

 uated anthrax vaccines at an interval of twelve days, and twenty-five 

 were left untouched. Twelve days afterward the two groups of twenty- 

 five sheep were inoculated with virulent anthrax; and the result was 

 that at the next visit the twentv-five unvaccinated and one vaccinated 



