I crossed the lawn and entered a large waiting-room occupying the middle of the building devoted to laboratory work. The room is flooded with light, seated with benches, and decorated with no other ornaments than a series of photographs of the Pasteur Institute at Rio Janeiro, two great maps on which are marked the cities where institutions similar to this at Paris are to be found, and cards containing certain rules applicable to patients coming for treatment against hydrophobia. Among these latter the important ones are that the treatment is gratuitous, that each patient must bathe before coming for inoculation, that board and lodging are not furnished, and that the grateful may, if they wish, leave a gift at the end of their term of treatment. There were sixty or seventy persons in the room. They had come to be vaccinated against hydrophobia. They were of the greatest contrast in age, in condition, in culture. Beside a shrivelled, leather-brown Arab woman from the desert was a pink and white little miss from London. A young man with the refined face, correct dress and distinguished manners of a gentleman sat beside a huge and none-too-clean German laborer. As a rule, it was a friendly, cheerful company. It was only here and there that one saw a person who seemed conscious that in his veins a hideous poison was at work. Most of them took it for granted that their cure was certain. Some of them scoffed at the nonsense of going to the trouble of being vaccinated. A dignified liveried servant entered, calling "Attention." The company bestirred itself and disappeared. I made my way to the inoculating room. The operation of inoculating for hydrophobia is founded on the theory that if an "attenuated" microbe, that is a microbe so treated that its power of doing harm has been reduced to a low degree, is introduced into a body, it will produce an indisposition which is not itself serious, but which is sufficient to render the body proof against attacks of the original microbe. Now M. Pasteur has discovered that it is possible to so treat a microbe that its power of evil is of any degree; that is, to "exalt" as well as to "attenuate" it. Having these microbes of varying strengths he invented a method of graduated vaccination; that is, by beginning with a virus of low degree, and increasing each day the strength of the virus, an operator arrives at a point where he can vaccinate a body with a virus stronger than there is any danger of its ever being exposed to in nature. He thus secures lasting immunity. Thus, in vaccinating against rabies, the patient is treated first with a weak virus; this is followed by one more powerful, and so on, until at the end a highly "exalted" one is injected safely. [Illustration: M. PASTEUR AT THIRTY.] It is this treatment which is practised daily at the Pasteur Institute, in the inoculation room where I found myself.