INSERTION is the application of the variolous matter to some part of the human body. It is well known, that this application takes effect only on some sensible part; therefore, if it is made externally, it must be under the cuticle or scarf-skin, which is an insensible membrane. It is likewise known, that the activity of the virus is so prodigious, that the smallest atom, imperceptible either by sight or feeling, conveys the small-pox equally well with a large quantity.
Hence the most obvious way to perform this operation seems to be, to prick the skin slightly with a pin or needle dipt into a variolous pustule. As nothing is requisite to infuse the poison into the animal system, but to introduce it beyond the scarf-skin, a slight puncture, which divides the membrane, must have appeared sufficient to the earliest operators. The dreadful effects of the poison, which these inoculators had observed in the natural small-pox, could not but make them sparing of it in their first attempts; and tender parents would naturally be equally fearful, and unwilling to put their children to unnecessary pain.
Accordingly we find that, at the first origin of inoculation, in several countries, but especially in those where it was performed by women, the insertion was made in that simple