Inoculation ('engrafting'), the communication of disease to a healthy subject by the introduction of a specific germ or animal poison into his system by puncture or otherwise, originally used of the inoculation of smallpox (for preventive inoculation, see BACTERIA, GERM, ANTHRAX, DIPHTHERIA, HYDROPHOBIA). If the matter of a smallpox pustule, taken after the commencement of the eighth day, be inserted in or beneath the skin of a person who has not previously suffered from smallpox, the following phenomena are induced: (1) Local inflammation is set up; (2) on the seventh or eighth day there is fever similar to that of smallpox; and (3) after the lapse of three more days there is a more or less abundant eruption of pustules. This process is termed inoculation, and the disease thus produced is denominated inoculated smallpox. The disease produced in this artificial manner is much simpler and less dangerous than ordinary smallpox; and as it was an almost certain means of preventing a subsequent attack of the ordinary disease, inoculation was much practised till it was superseded in the beginning of this century by Jenner's introduction of vaccination. The importance of inoculation was recognised in the East at a very early period, the Chinese practising it from the 6th century, and the Brahmins from a very remote antiquity. In Persia, Armenia, and Georgia it was in use, and it is even said to have been employed in Scotland and Wales. It was not, however, till Lady Mary Wortley Montagu wrote her celebrated letter from Adrianople in 1717 that the operation became generally known in England. In that letter she writes: 'The smallpox, so fatal and so general amongst us, is here entirely harmless, by the invention of ingrafting, which is the term they give it. Every year thousands undergo the operation. There is no example of any one that has died in it, and you may believe that I am very well satisfied of the safety of the experiment, since I intend to try it on my dear little son.' Four years afterwards she had her daughter publicly inoculated in England; the experiment was then performed successfully on six condemned criminals at Newgate, and on the strength of these successful cases two children of Caroline, Princess of Wales, were inoculated, which gave a sanction to the practice.
Inoculation was not, however, thoroughly established for more than a quarter of a century after its introduction. It met with virulent opposition both from the medical profession and the clergy. A sermon is extant which was preached in 1722, by the Rev. Edward Massey, in which it is asserted that 'Job's distemper was confluent smallpox, and that he had been inoculated by the devil.' The great drawback to inoculation turned out, however, to be this: while it was invaluable to him who underwent the operation, and completely guarded him from the natural disease in its severe form, its effect upon the community at large was extremely pernicious in keeping alive the natural disease, and increasing its spread amongst those who were not protected by inoculation. While one in five or six of those who took the natural disease died, the average number of deaths at the Inoculation Hospital was only 3 in 1000; and yet, according to the authority of Heberden, in every thousand deaths within the bills of mortality in the first thirty years of the 18th century (before inoculation was at all general) only seventy-four were due to smallpox. The deaths from this disease amounted to 95 in 1000 during the last thirty years of the century; so that, notwithstanding the preservative effects of inoculation on almost all who were operated on, the total number of deaths from this disease increased in one hundred years in the ratio of about 5 to 4. At the beginning of the 18th century about one-fourteenth of the population died of smallpox; whereas at the latter end of the same century the number (notwithstanding, or perhaps rather in consequence of, inoculation) had increased to one-tenth; and this immense consumption of human lives was not the total evil, for many survivors were left with the partial or entire loss of sight and with constitutions destroyed. The benefits which were expected from inoculation were far from being realised, and smallpox would doubtless have gone on increasing in its destructive power if it had not been checked by Jenner's discovery of Vaccination (q.v.). Inoculation was forbidden by law in 1840.