"Virulence is a quality that microbes can lose, or can acquire. Suppose we came across the anthrax-bacillus so far attenuated, in the way of Nature, that it had lost all power to kill--of course we should fail to recognise it; we should take it for an ordinary bacillus of putrefaction: you must watch it through each phase of its attenuation, to know that the harmless organism is the descendant of the fatal virus. But you can give back to it the virulence that it has lost, if you put it, to begin with, under the skin of a very delicate subject, a mouse only one day old. With the blood of this mouse inoculate another, a little older, and it will die. Passing by this method from younger to older mice, we come to kill adult mice, guinea-pigs, then rabbits, then sheep, etc. Thus, by transmission, the virus gains strength as it goes. Doubtless this increase of virulence, that we bring about by experiment, occurs also in Nature; and it is easy to see how a microbe, usually harmless to this or that species of animals, might become deadly to it. Is not this the way that infective diseases have appeared on the earth from age to age? "_See how far we have come, from the old metaphysical ideas about virulence, to these microbes that we can turn this way or that way--stuff so plastic that a man can work on it, and fashion it as he likes._" Pasteur's note on the attenuation of anthrax was presented to the Académie des Sciences on 28th February 1881; and the test-inoculations at Pouilly-le-Fort were made in May of that year. It was hardly to be expected that every country, in every year, should obtain such results as France now takes as a matter of course; and at one time, about twenty-one years ago, there was in Hungary a "conscientious objection" to the inoculation of herds against the disease. But in Italy, from 1st May 1897 to 30th April 1898, the issue of anti-charbon vaccine from one institute alone, the Sero-Therapeutic Institute at Milan, was 165,000 tubes, enough to inoculate 33,734 cattle and 98,792 sheep. And in France, between 1882 and 1893, more than three million sheep, and nearly half a million cattle, were inoculated. The work done in France was published by M. Chamberland, in the _Annales de L'Institut Pasteur_, March 1894. The following translation of his memoir--_Résultats pratiques des Vaccinations contre le Charbon et le Rouget en France_--shows something of the national influence of the Pasteur Institute:-- 1. _Charbon_ "After the famous experiments at Pouilly-le-Fort, MM. Pasteur and Roux entrusted to me the whole method and practice of the vaccinations against _charbon_. Twelve years have passed, and it is now time to put together the results, and to make a final estimate of the value of these preventive inoculations. "Every year we ask the veterinary surgeons to report-- 1. The number of animals they have vaccinated.