Inoculation, the transmission of a disease from one individual to another by means of a morbific matter taken from the body of the first and introduced into the system of the second. The morbific matter may be introduced directly into the tissues by means of an incision or puncture in the skin, or it may be applied in a fiuid form to an abraded surface, from which it is absorbed by the skin itself. There are only certain diseases which are communicable in this way, the simple inflammations and their products not having the power to breed a similar malady in a healthy person. But there are particular specific diseases, such as smallpox, cowpox, primary syphilitic and gonorrhoea! inflammations, and the like, the exudations of which are charged with a peculiar organic virus which when introduced into the system of another individual gives rise to a disorder like that by which it was originally produced. Vaccination is simply the inoculation of vaccina or cowpox; and the term inoculation is sometimes restricted in common parlance to the intentional communication, by this means, of smallpox in its original form.

The inoculation of smallpox was early found to mitigate the severity of the disease; but vaccination was afterward substituted for it (see Jenner), because vaccina, though milder still, was discovered to be an effectual protection against smallpox itself.