A great impetus was given to inoculation in England by the letters of Lady Mary Wortley Montague, the wife of our ambassador to Turkey, Edward Wortley Montague, and daughter of the Duke of Kingston. In 1717 Lady Mary wrote a letter to her friend Miss Chiswell, in which she explained the process and promised to introduce it to the notice of the English physicians. So convinced was Lady Mary of the safety of smallpox inoculation and its efficacy in preserving from subsequent smallpox, that in March, 1717, she had her little boy inoculated at the English embassy by an old Greek woman in the presence of Dr. Maitland, surgeon to the embassy. In 1722 some criminals under sentence of death in Newgate were offered a full pardon if they would undergo inoculation. Six men agreed to this, and none of them suffered at all severely from the inoculated smallpox. Towards the close of the same year two children of the Princess of Wales were successfully inoculated; and in 1746 an Inoculation Hospital was actually opened in London, but not without much opposition. As early as 1721 the Rev. Cotton Mather, of Boston (U. S. A.), introduced inoculation to the notice of the American physicians, and in 1722 Dr. Boylston, of Brooklyn, inoculated 247 persons, of whom about 2 per cent. died of the acquired smallpox as compared with 14 per cent. of deaths amongst 6,000 uninoculated persons who caught the natural smallpox. There was, however, great popular opposition to the practice of inoculation, and Dr. Boylston on one occasion was nearly lynched.
While successful inoculation undoubtedly protected the person from smallpox, sometimes the inoculated form of the disease was virulent, and certainly all cases of inoculated variola were as infectious as the natural variety. Inoculated persons were therefore a danger to the community; and there is no doubt that such persons had occasionally introduced smallpox into towns which had been free from the natural disease. At the end of the eighteenth century, just about the time of Jenner's discovery, public opinion was strongly against the continuance of the practice of inoculation, and as natural smallpox had not at all abated its epidemic character, the times were ripe for "some new thing."
Now there is a disease of cows know as cowpox or vaccinia (from the Latin vacca, a cow) which is communicable to human beings. It is thought to be due to the same virus which in pigs is called swinepox and in horses "grease." Jenner believed vaccinia to be the same pathological entity as human smallpox, modified, however, by its transmission through the cow. For a long time this view was stoutly resisted, but it has now been accepted as probably representing the truth. The identity of vaccinia and "grease" is certainly much more doubtful.
To many of Jenner's contemporaries the view that vaccinia had at one time been a disease of human beings seemed unlikely; but we are now in a far better position to admit its probability than were those of Jenner's time. We have since then learned that man shares many diseases with the lower animals, tuberculosis, plague, rabies, diphtheria and pleuro-pneumonia, to mention only a few. We have also learned that certain lower animals, insects for instance, are intermediary hosts in the life-cycle of many minute parasites which cause serious diseases in the human being, amongst which malaria, yellow fever and the sleeping sickness are the most familiar.
It appears to have been understood before Jenner's time that persons who had acquired cowpox by handling cattle, but especially by milking cows, were immune from smallpox. In the reign of Charles II. it is well known that the court beauties envied the dairy-maids because having had cowpox, they could not take smallpox which all women so dreaded. Dr. Corlett tells us that the Duchess of Cleveland, one of the King's mistresses, on being told that she might lose her place in the royal favor if she were disfigured by smallpox, replied that she had nothing to fear as she had had cowpox. In 1769 a German, Bose, wrote on the subject of cowpox protecting from smallpox. In the year 1774 a cattle dealer, Benjamin Jesty, at Yetminster, in Dorset, inoculated his wife and three children with cowpox. None of them ever took smallpox during the rest of their lives although frequently exposed to its infection. Jesty died in 1816, and it is recorded on his tombstone that he was the first person who inoculated cowpox to protect from smallpox. Cowpox, or vaccinia, though infectious for cows, is not transmissible among human beings, in other words, as a disease of man it is not infectious. Edward Jenner, the Englishman of Berkeley in Gloucestershire, was the first person to think scientifically on the fact that cowpox protected from smallpox. John Hunter had said to him, "Jenner, don't think, try." Luckily, however, he did both. Thinking alone avails little, experimentation alone avails not much, but the one along with the other has removed mountains. Just as Newton thought scientifically about that falling apple and reduced our conceptions of the universe to order, just as Watt thought scientifically about that kettle-lid lifted by the steam and so introduced the modern era of mechanical power brought under man's control, so Jenner thought about and experimented with cowpox until he had satisfied himself that he had discovered something which would rid the human race forever of the incubus of an intolerable pestilence.
It was in 1780 that Jenner set himself to study cowpox in a way that had never before been attempted, for he was convinced that in the having had an attack of the disease lay the secret of the conquest of that world-scourge. He confided in his fried Edward Gardner about "a most important matter . . . which I firmly believe will prove of essential benefit to the human race . . . should anything untoward turn up in my experiments, I should be made, particularly by my medical brethren, the subject of ridicule." Luckily he was quite prepared for both ridicule and opposition; for has not everything new been ridiculed and opposed? Galileo was opposed, Bruno was opposed, Copernicus was opposed, Harvey was opposed, George Stevenson was opposed, Pasteur was ridiculed and opposed, and so were Darwin, Simpson and even Lister. The physiological inertia even of the educated has too often blocked the path of advancement: but Jenner is in illustrious company, a prince amongst the hierarchy of the misunderstood.
The facts or surmises before Jenner at this date, then, were—(a) Cowpox produces an eruption extremely like that of mild smallpox, it is, therefore, probably a form of smallpox modified by transmission through the cow; (b) And an attack of cowpox protects from smallpox. To test these things experimentally some one must first be inoculated with cowpox, and, having recovered from the vaccinia, that same person must, secondly, be inoculated with the virus of smallpox or be exposed to the infection, and, thirdly, this person ought not to take the disease.
In 1788 Jenner had a careful drawing made of the hand of a milkmaid suffering from cowpox to demonstrate to Sir Everard Home how exceedingly similar were vaccinia and variola. Home agreed it was "interesting and curious," and the subject began to attract some attention in medical circles.
In November, 1789, Dr. Jenner inoculated his eldest child Edward, aged 18 months, with some swinepox virus, and as nothing untoward happened, he inoculated him again with swinepox on April 7, 1791. The child had a slight illness, very like vaccinia, from which he rapidly recovered. The moment for the crucial experiment was not yet; it came in due time, but Jenner had to wait five years for it, and five years are a long time to a man who is yearning to perform his crucial experiment. Happily for suffering humanity, in the early summer of 1796 the opportunity came; the hour and the man were there together.
Cowpox had broken out on a farm near Berkeley and a dairy maid called Sarah Neames contracted the disease. On May 14, 1796, Dr. Jenner took some fluid from a sore on this woman's hand and inoculated it by slight scratching into the arm of a healthy boy eight years old, by name James Phipps. The boy had the usual "reaction" or attack of vaccinia, a disorder indistinguishable from the mildest form of smallpox. After an interval of six weeks, on July 1, Jenner made the most momentous but justifiable experiment, for he inoculated James Phipps with smallpox by lymph taken from a sore on a case of genuine, well-marked, human smallpox, AND THE BOY DID NOT TAKE THE DISEASE AT ALL. Jenner waited till the nineteenth of the month, and finding that the boy had still not developed variola, he could hardly write for joy. "Listen," he wrote to Gardner, "to the most delightful part of my story. The boy has since been inoculated for the smallpox which, aS I VERNTURED TO PREDICT, produced no effect. I shall now pursue my experiments with redoubled ardor."