Hayden — On Respiration of Compressed Air. 205 
''Dr. Jaminet on one occasion remained in two and three quarter 
hours, when the depth was over ninety feet, and was dangerously- 
attacked soon after reaching home. 
"Symptoms of paralysis rarely occurred in the shaft, but gene- 
rally after the stairs were ascended, and never in the air-lock or air- 
chamber." 
The importance to the present subject of the preceding extracts, 
both in regard to the facts stated, and the inferences drawn from 
them, is my apology for their great length. The amount of informa- 
tion in physiology, and the critical acumen which the writer has 
exhibited in the observations just quoted, are eminently creditable 
to him. 
Before I proceed to discuss the opinions enunciated by him, 
and make some general remarks on the subject under consideration, I 
wish to supplement what has been taken from the chief engineer's 
Report, by some very pertinent observations contained in Dr. O'Reilly's 
letter. He says: — "Aside from its importance in showing the ob- 
stacles which modern engineering science can overcome, by construct- 
ing the piers of a bridge of such magnitude as to support spans of five 
hundred and fifteen feet, sinking them as they build from above 
downwards, through water and sand one hundred and fifteen feet 
deep, to the rock-foundation, with a strong current equal to six miles 
per hour, and the atmospheric pressure in the caisson, or chamber 
under the pier, in which the workmen shovel the sand to the pumps, 
by which it is gradually sunk to the bottom, is equal to four atmo- 
spheres, or say sixty pounds to the square inch ; it is important to the 
physiologist, as this unusual pressure in the human body has de- 
veloped a train of symptoms pretty accurately described in the engi- 
neer's Report. 
"I sawmany of the men afflicted with the painful feelings described, 
and their agony was very great ; but I found nothing to relieve them, 
except the subcutaneous injection of morphine, and hypnotic doses of 
the chloral hydrate. I do not think that the galvanic armour men- 
tioned by Colonel Eads had the slightest advantage beyond its moral 
effects as a diversion to the mind. None of those I attended died, 
and I was not present at any of the pod mortem examinations." 
Unfortunately the Report contains no account of the structural 
lesions, if any, exhibited by those who died from the effects of exposure 
to compressed air, and no statement of the per centage of carbonic acid 
in the air expired under the pressure of four atmospheres. I hope to 
obtain some additional information on this part of the subject, and if 
successful in my endeavours I shall have much pleasure in sub- 
mitting it as a supplement to this Paper at a future meeting of the 
Academy. 
According to Vivenot the inhalation of compressed air reduces the 
frequency of the pulse on the average about six and a half pulsations in 
the minute. This effect he attributes to the mechanical pressure 
of the heavier air on the surface of the body, and consequent reduction 
