Hayden — On Resjoiration of Compressed Air. 199 
XXXI. — On the Eespieation op Compressed Aie. By Thomas 
HAYDEJf, F. C. P. &C. 
[Read 26tli June, 1871.] 
Foe normal respiration, so far as it relates to the atmosphere, three 
conditions are necessary — an adequate supply of dilute oxygen, com- 
parative freedom from gaseous impurity, and a state of equilibrium 
between the gases contained in the blood and tissues of the body, and 
the surrounding air. 
I do not propose to discuss the two former conditions in this 
Paper ; but in regard to the latter, derangement of equilibrium may 
take place, either by rapid reduction, or by rapid augmentation of 
barometric pressure. 
As a consequence of rapid diminution in the density of the air 
breathed, the group of phenomena constituting the Mai de Montagnes 
is exhibited. These are — I^ausea, headache and vertigo, great diffi- 
culty of breathing, palpitation and panting, accelerated pulse, tinnitus 
aurium, a feeling of lassitude and dejection, somnolence, bleeding from 
the gums and lips, and suffusion of the conjunctivae ; as determined by 
Humboldt and his companions, and by a host of subsequent observers, 
at great altitudes. 
Lepileur declares that these symptoms entirely disappear after a 
certain time under the same barometric pressure, so that inconvenience 
is no longer experienced, the organism having accommodated itself to 
the altered circumstances in which it is placed. In other words, 
the barometric equilibrium between the gases permeating the body 
and the surrounding atmosphere, is re-established. 
The inhabitants of high regions find themselves normally under 
these conditions, and experience no particular inconvenience there- 
from. Thus, in Deba, in Thibet, the residence of a Lama, which 
is nearly 5000 metres above the level of the sea, and about the same 
height as the summit of Mont Blanc, atmospheric pressure is re- 
duced to about one-half, yet the inhabitants suffer no special incon- 
venience. 
Longet considers that the too sudden diminution of atmospheric 
pressure must profoundly modify oxygenation, and so produce the 
above-mentioned consequences — a certain time being necessary for the 
readjustment of the balance between the gases of the blood and those 
external to the body. 
It is remarkable that aeronauts, who ascend much more rapidly 
into the higher regions of the atmosphere, by no means experience in 
the same degree the symptoms of the Mai de Montagues. This diffe- 
rence is probably due to the state of quiescence of body in which they 
are placed, comparatively with those who, by great muscular efforts, 
make the ascent of high mountains. 
