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.

Let me begin, then, by stating that my attention was attracted several
years ago by that unique complex of symptoms known as the "caisson or
tunnel disease." As most physicians are aware, the caisson disease is
an affection of the spinal cord, due to a sudden transition from a
relatively high atmospheric pressure to one much lower. Hence, those
who work in caissons, or submerged tunnels, under an external pressure
of two atmospheres or even more, are liable to be attacked by the
disease shortly after leaving the tunnel. The seizure never, however,
occurs while the subject is in