Hayden — On Eesjnration of Compressed Air. 207 
time, as mentioned by all observers, this pain ceases, manifestly owing 
to the penetration into the cavity of the tympanum, of the condensed 
air by way of the Eustachian tube. The entrance of air to the middle 
ear by this devious and compressible passage requires a short time for 
its accomplishment, but may be instantaneously effected by an act of 
swallowing, by which the tube is for a moment expanded, or by in- 
flation of the pharynx, as stated and correctly explained by Colonel 
Eads. The return for a moment of the aural pain on passing into the 
normal atmosphere was due to a fresh derangement of gaseous equili- 
brium, but now by a transposition of the inequality. 
The nasal character of the voice, and the inability to whistle, would 
seem mainly due to the necessary modification of elasticity in the con- 
densed air, by which its capacity to propagate sonorous vibrations was 
altered in a proportionate degree ; but impairment of contractile power 
in the muscles of the palate and lips, by reason of the heavy atmospheric 
pressure born by them, probably contributed in some degree to this 
result. 
Paralysis of the voluntary muscles was most likely due in greatest 
part, if not exclusively, to muscular exhaustion ; and this opinion would 
seem borne out by the statement of Colonel Eads, to the effect that it 
occurred in no instance in which the subject of it had not performed 
protracted duty in the condensed air-chamber, and that in all cases 
where death did not actually follow, it was of very brief duration, not 
exceeding in any case a period of two days. Depression of body-heat 
would follow impairment of the respiratory function, whilst sensible 
and copious perspiration would obviously result from the diminished 
hygrometric capacity of highly condensed air. 
The normal exhalation of carbonic acid amounts to about 4' 35 per 
cent of the expired air, and the decrease consequent on the respiration 
of compressed air might be accounted for, at least in part, by a notable 
reduction of more than two per cent, in the proportion of oxygen in 
that air. 
Itnow only remains for me to discuss the dilatation of the pulmonary 
structure, and to make a few concluding remarks on the therapeutic 
applications of compressed air. 
A state of equilibrium of the ultimate pulmonary structure, admit- 
ting of alternate contraction and dilatation, strictly proportioned to 
the mobility of the chest walls, is not only normal to it, but likewise 
essential to its functional efficiency. This state is the result of two 
opposing and usually well balanced forces, one tending to expand, and 
the other to contract or reduce the volume of the lungs. " The former 
of these forces consists of the active expansion of the chest by the 
muscles of inspiration, supplemented by the elastic expansion of the 
air within the lungs under the influence of the normal heat of the 
body; and the latter, ordinarily of the passive or elastic reaction of 
the chest walls, aided by that of the lungs. A still further reinforce- 
ment of either of these agencies by any cause whatever, would derange 
the balance of respiration, and constitute a morbid condition. Mani- 
