the caisson, or in other words, while
he remains under pressure. Moreover, when the transition from the
condensed atmosphere to that of ordinary density is gradually
accomplished, which may be done by letting the air escape from the
lock very slowly, the caisson disease is rarely if ever set up. It is
the systematic disregard of this principle by those who work in
compressed air that is responsible, or largely responsible, for the
occurrence of the disease.

The chief clinical features of the caisson disease are pain, which may
be relatively mild, as when confined to a circumscribed area of one
extremity, or of frightful intensity, as when it appears in the ears,
knees, back, or abdomen; anaesthesia and paralysis, usually of
paraplegic type; bladder symptoms, assuming the form of retention or
incontinence; and, more rarely, rectal disturbances (usually
incontinence).

These phenomena, or rather some of them, appear some time within half
an hour after the subject has left the compressed atmosphere. It was
while investigating this most interesting affection as it occurred in
the course of the construction of the Hudson River tunnel, that I was
able, at the same time, to study the effects of compressed air upon
the organism, and especially upon the nervous system, as exhibited in
a large number of persons.

The results of these studies I now submit without hesitation, and in all
candor, to the judgment of the profession, believing, as I certainly do,
that their practical significance from a neuro-therapeutic standpoint is
assured. Without anticipating, however, let me state that the first
thing which impressed me about compressed air was its extraordinary
effect upon cerebral and cerebro-spinal function.

Those who remain for a certain length of time, not too long, however,
in the condensed atmosphere, exhibit a most striking exacerbation of
mental and physical vigor. They go up and down ladders, lift heavy
weights, are more or less exhilarated, and, in short, behave as though
under the influence of a stimulant.

Hardly had I observed these things, which are perfectly well known to
those who have been able to familiarize themselves with the ordinary
effects of compressed air as used in caissons and submarine works of
various kinds, when my attention became attracted by what at first
appeared to be a phenomenon of trivial importance. In a word, I
observed that some of the men exposed to the effects of the compressed