It was easy, therefore, to notice in this case, as was indeed very early done in the East, that a person who has gone through one attack, as shown by his pitted face, very rarely suffers even during severe subsequent epidemics. Smallpox, like other epidemic diseases, breaks out in some years in very fatal, in others in milder forms. It is admissible that by a mixed process of thought and faith an impression insensibly gained ground that it was _lucky_ to have been touched by the smallpox deity--of course, not in years when that deity appeared in terrifying mortality. Accordingly, in times of _mild_ outbreaks people would not be very careful in avoiding infected persons, and would even seek their company so as to get infected from them. The practice of intentionally rubbing one’s skin with a pustule, or with bits of it, from an attacked person, must have been a subsequent stage. Such or a similarly gradual development of ideas may explain why it is impossible to fix a date or place for this discovery, which indeed goes back to the darkness of antiquity. Research points to its practice among the Chinese and Hindus in very ancient times. The Chinamen induced a mild attack by inserting a crust from a smallpox pustule into the nostrils. The Hindus, on the contrary, used the fluid pus, which they inoculated under the skin of the arm. In either case, in the course of a week, the inoculated was attacked by some slight preliminary symptoms followed by an eruption, sometimes profuse, sometimes scanty, and then the disease would run its ordinary course. The only difference between an attack caused by inoculation and that caused by natural infection was, as a rule, the milder nature of the former, especially when the matter for inoculation was taken from a notoriously mild case. The result, however, was by no means certain. A mild form of an infectious disease may be due either to the virus being of a weak nature; and then such a virus would be the desired one for inoculating persons seeking artificial protection; or else the mildness of the case may be due to the patient himself being of a resistant organization, in which case, though exhibiting mild symptoms himself, he may be harboring an intense form of contagion, apt to cause a severe outbreak when transferred to other less resistant persons. Many plans were consequently adopted to secure with more certainty a mild artificial infection. Some of these were directed to the treatment of the patient preparatory to inoculation, others to the preparation of the infectious matter in order to attenuate its virulence. The Brahmans, who were the operators in India, in addition to selecting material from patients with a mild form of the disease, were accustomed not to employ the pus at once, but to keep it wrapped up in cotton wool for a period of about twelve months, and thus to weaken its power. They inoculated in the early part of the year, at the time when smallpox