Although it is impossible to determine geometrically the degree of health requisite for inoculation, you may safely trust to that indeterminate judgment we commonly pass, when we say, such a one is well: we mean that nothing amiss is observable, nothing at least that attacks the vital functions, nor any tendency to sickness, as in children during dentition, or women during pregnancy, &c.
But besides this general rule, the fitness for inoculation may be determined with greater certainty by a few plain and easy signs; viz. 1. the sweetness of the breath; 2. the thinness of the skin; 3. the facility of cicatrisation. I do not know whether these signs only indicate the state of which we call health, or whether they denote those unknown qualities, which are favourable to the action of the virus: but certain it is, that I have always found them to be attended with a mild small-pox, in proportion to the degree in which they were observed.
