Still, he had the satisfaction of seeing compulsory vaccination established in many of the countries of Europe, and knew that it was making its way among enlightened peoples everywhere, before his death in 1833, which occurred in his native rural home, where he had returned after a short and distasteful residence in London. Ten days before his death he got a letter, on the back of which he wrote the following: "My opinion of vaccination is precisely as it was when I first promulgated the discovery. It is not in the least strengthened by any event that has happened, for it could gain no strength. It is not in the least weakened, for if the failures you speak of had not happened, the truth of my assertions respecting the coincidences which occasioned them could not have been made out."
In the seventy years since, evidence has accumulated as to the inestimable value of the original discovery; wide observations among thoroughly trained medical men have also demonstrated the value of revaccination—after maturity—of persons who had been vaccinated in infancy; but the most glorious result of all was to be the illumination of Pasteur's great scientific mind, as to the possibility of the production of a modified virus in other diseases than smallpox.
Modern science contains no more interesting chapter than the one which shows how that, after the achromatic compound microscope—magnifying close on to two thousand diameters—was put into the hands of scientists, step by step it was shown that what we call zymotic or "catching" diseases are caused by the living germs of parasitic plants entering the blood, and there multiplying and growing, deriving the needed sustenance from the blood itself. Pasteur caught the idea of a modified growth from Jenner's experiments, as he distinctly said in his original paper on anthrax, read before the French Academy. That it is within the power of man to modify plants outside the body, any one who has tasted a native astringent crab and a delicious Baldwin apple will believe, but it remained for a devotee of science for its own sake—like Pasteur—to observe and experiment and think till he achieved that "attenuated virus" which annually saves millions of animals in Europe from the ravages of anthrax, and multitudes of men from death by hydrophobia through the bites of wolves, dogs, and cats. The statistics of the Pasteur Institute of Paris show that in the five years from January 1, 1886, no less than nine thousand four hundred and thirty-three persons were treated, of whom fifty-eight died, or 0·61 per cent. The instrument of this merciful exemption was a modified—i. e., attenuated—virus.
With such results, such victories of the wit of man over Nature, while bacteriology is yet in its early infancy, it is no wonder that Pasteur predicts the time when "these diseases will be
