INOCULATION, in Medicine, the artificial produc tion of an infectious disease by morbific matter, brought in contact with the animal fibre. This is practised for the sake of inducing a milder form of disease than that which is the general consequence of casual infection, and for pro tecting the constitution against future attacks of the same disease.
Inoculation has been performed for the sake of experi ment, in various diseases which are known to attack the human frame only once, but in none with that marked suc cess which has taken place in small-pox. Wherever it has been practised, it has greatly diminished the mortality arising from that disease ; and hence has, for nearly a cen tury, been in general use as a preventive of its dangerous forms.
Inoculation comprehends some of the most curious phe nomena of physiological and pathological science, and therefore becomes interesting, both in a scientific and a practical view. We do not know all the causes of the dif ferences in degrees of mildness of the same disease. Phy sicians are most generally inclined to ascribe them to pre vious differences in the state of the constitution of the per son affected. It could not have been concluded, and scarcely even surmised a priori, that a difference in the mode in which the morbific matter was applied, would have in this respect any marked effect. Far less could it have been supposed, that matter, in a fixed and moist state, brought in contact with an exposed living part, would have produced a disease milder than that which is generated by dry contagion, casually applied to the cuti cle or volatile effluvia inhaled in respiration. These points of doctrine ate only known in consequence of continual ex perience. It might be expected, that some extension of the knowledge of this law of contagion might enable us to insure to the attendants of the sick a mild, rather than a severe form of other contagious diseases, where one or the other is unavoidable ; but as yet we know nothing more than the gross facts connected with inoculation as ac tually practised. Even a plausible rationale of the well known result is a desideratum in medical science. It might be ascribed to the minuteness of the quantity of mat ter introduced ; but this is hardly a probable theory, and does not seem in perfect accordance with some other facts attending the communication of contagious diseases. But it is highly satisfactory to find, that the beneficial effects of inoculation are so undoubted and so extensive in ex empting society from the incursions of one of the most desolating diseases, or reducing the mortality of it '. ith
in an incomparably narrower compass. It will, therefore, be interesting to take a retrospect of the history of this va luable discovery.
The small-pox had prevailed for several centuries in ci vilized Europe, before inoculation was generally know n. It is not, however, one of the most ancient diseases. It was not known to Hippocrates, our any ef the old Greek or Roman authors. It is first mentioned by the Arabians, after the establishment 01 the Mahomedati religion. The mode and principles of its production must, like all other points of the same kind, remain to us unknown, and the Formation of conjectures on such a subject is a fruitless ap plication of inventive genius. The existence of it cannot be traced farther back than to the siege of Alexandria in 640. But whether it originated among the besieged Lgyp tians or their Arabian invaders, is not known. We are in deed told that traces of it have been found in some Chi nese writings of much more ancient date, and also in some of the sacred books of the Gentoos ; but these accounts are too general to prove the high antiquity of the disease, and are equally unworthy of confidence with the fanciful com ments by which -a similar testimony has been extorted from the Jewish write' a. The only accounts worthy of being listened to are tIose in which this disease is said to have attacked the army of the Arabian and Abyssinian Chris tians at the siege of the pagan city of Alecca, in 522, about the time of the birth of Nlahomet. But it was certainly unknown to the most intelligent w titers till the siege of Alexandria by the Saracens. The history of its subse quent ravages was but imperfectly recorded. We only find occasional traces of them. Circumstances of that kind are often omitted in the historical page, but we have enough to show that this was one of the most formidable diseases to which society was exposed. Many persons of distinction arc casually mentioned as having fallen vic tims to it. The time of its first introduction into Bri tain is not precisely known, but both here, and in every other country, it has been peculiarly destructive when it made its first appearance. It is said to have been import ed to Europe by the crusaders ; but it appears to have been of much earlier introduction. In 1520, it first visited some provinces of South America, and proved fatal to one half of the inhabitants. In Europe it continued to he, till the last century, the principal risk to which human life was exposed at an early age.