b. Its fatality is comparatively small, so that after each outbreak a large number of convalescent persons remain alive to serve as objects for future observation and comparison.
c. These convalescents are marked and are thus easily distinguishable from the rest of the population who have not been attacked, and even the severity of the disease they have gone through is, so to say, written down on their faces and bodies.
d. The disease is easily communicable, owing to the infectious matter appearing on the surface of the patient’s body in the pustules.
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 prevailed, and the practice they used was to moisten with water a bit of cotton wool prepared in the previous outbreak, to place it on the arm of the person to be inoculated, and to prick the arm, through the wool, over an area of about the size of a twenty-five cent piece. In a few days a vesicle would appear at the seat of the inoculation, which later on developed into a pustule and eruption. Notwithstanding these precautions, great variation in the results was observed, and many succumbed to the operation; but those that passed through it safely were proof against further attacks.
Besides the personal risk to the inoculated, the illness produced in them was infectious to others, and unprotected persons coming in contact with the inoculated were likely to get infected from them. The latter result was largely avoided by the practice adopted by the Brahmans of inoculating all the inhabitants of a family or village at the same time. The benefits secured under the above precautions were considered far to outweigh the risks of inoculation.
With the extension of smallpox westward the system of artificial protection spread toward Europe through the intermediary of travelers and merchants. The Arabs and Turks appreciated its benefits at an early date. The slave dealers supplying the bazaars and harems of Constantinople adopted the system to protect against disfigurement their Circassian and other live stock. In the early part of the eighteenth century the method was made known to the English practitioners by Lady Mary Wortley Montagu, the wife of the English ambassador at Constantinople, who had her two children inoculated according to the Turkish system. Curiously enough, it was soon afterward discovered that a similar method was in practice among the peasants of some of the districts in Wales and the Highlands of Scotland, and had long been known there as ‘buying the smallpox.’ When inoculation was given a more extensive trial it was found, in England as in the East, that the effect of it was decidedly beneficial, but fraught with danger. At first one in every fifty of those operated upon succumbed to the consequences of inoculation. By improved methods the mortality was gradually reduced to one in a thousand; but the most serious danger lay in the spread of infection to healthy persons. The precaution of inoculating whole groups of inhabitants at one time, or of keeping the inoculated apart from the healthy, as had been practiced by the Brahmans ages ago, was overlooked, and the result was often disastrous to the community.
* * * * *
It was at this time that Jenner achieved great progress and threw a vast amount of new light on the question. As is well known, he started from a belief that existed in the west of England, that cowpox was a bovine form of smallpox, and that the milkers who attended on cows suffering from that disease and who became infected with the eruptions on the teats and udders, passed through a mild illness, which rendered them immune against smallpox. Jenner determined to put this tradition to the test, and succeeded in establishing, by a few accurate and well-planned experiments, a series of most important facts.
He showed, first, that cowpox could be artificially given to the cow by infecting it with virus from a smallpox patient, and that the disease thus produced was transferable by inoculation from cow to cow.