_Second Fact._--The duration of the effect of a remedy upon the cerebro-spinal axis is in the inverse ratio of its volatility; and this is equally true whether the remedy be given with or without the precautions previously detailed. For example, the anaesthetic effects of ether disappear shortly after removal of the inhaler, whether we apply tourniquets to the extremities or not; but, on the other hand, the analgesic influence of antipyrin, phenacetin, morphine, and other like remedies lasts very much longer, and their dose may be reduced, or--what is the same thing--their pharmaco-dynamic potency may be enhanced by the sequestration of the blood contained within the extremities. So far as I know, I was the first to announce this fact. In so far as a simple expression of the above truth is concerned, we may employ the following formula: Let _a_ represent the normal blood-mass contained in the entire body, _d_ the amount of blood sequestrated by the ligatures, _b_ the amount of the remedy, _c_ the volatility of the remedy, and _x_ the pharmaco-dynamic potency of which we are in search; we shall then have b x = ----------- (a - d') x c We now arrive at our third fact, which will require more extensive elaboration. _Third Fact._--The pharmaco-dynamic potency of stimulants, sedatives, analgesics, and probably of all remedies which possess a chemical affinity for nervous matter, is enhanced by exhibiting them (the remedies) in solution or soluble form--hypodermically, by the mouth, or per rectum--while the subject remains in a condensed atmosphere. And, as a corollary, it may be stated that this increase, this enhancement of the potency of the remedy is, within certain limits, in the ratio of the atmospheric condensation. To express this truth mathematically is not difficult. Thus, when a represents the amount of blood of the whole body, _b_ the amount of the remedy, _e_ the amount of atmospheric compression, and _x_ the pharmaco-dynamic potentiality which we are seeking, we shall then have the simple formula: b x e x = ----- a A definite conception of the truth of this proposition will, I think, be more readily attained by the presentation of the steps which led me to its discovery.