JULY 30, 1897.] 
us suppose that the usual pressure is reduced 
to one-half, then the rapidity with which the 
lungs are expanded, although still greater 
than the usual rate of the chest expansion, 
is yet only half as rapid as when under the 
customary atmospheric pressure, and under 
certain circumstances this may seriously 
disturb inhalation. 
Exhalation, on the contrary, is accelerated 
by the lighter pressure of a rarefied atmos- 
phere. It generally takes place without 
the aid of the muscles which assist in the 
process of inhalation. The expanded parts, 
_ as the lungs, diaphragm, etc., contract to 
their original size and position by reason of 
their elasticity, as soon as the muscular 
foree which was applied during inhalation 
is relaxed. The employment of the ab- 
dominal and intercostal muscles as an aid 
to exhalation is exceptional. 
The only obstacle which retards the con- 
traction of the lungs is the pressure of the 
outer air, which resists the outflow of the 
air from the windpipe and is diminished 
as the atmosphere becomes rarefied. Con- 
sequently the contraction of the lungs is 
greater and more rapid in ararefied atmos- 
phere. Exhalation is, therefore, in general, 
a mechanical process, and as such is subject 
to a certain law acording to which it can 
be performed on the summit of Mount 
Blane in 58, of the time required under the 
ordinary atmospheric pressure. 
Humboldt tells us that newcomers in the 
vicinity of Quito, Heuador, where the alti- 
tude is between 2,600 and 3,600 meters 
(11,800 ft.), have considerable difficulty in 
breathing, especially when talking rapidly. 
This is explained by the fact that the supply 
of breath usually reserved for the formation 
of sound escapes more rapidly and is there- 
fore sooner expended. It has also been 
observed that some persons are unable to 
whistle where the pressure has only been 
diminished from 760 mm. (ordinary atmos- 
pheric pressure) to500mm. The whistling 
SCIENCE. 
159 
sound is produced by placing the lips in a 
certain position, and depends upon the 
rapidity with which the air is forced out of 
the lungs by means of the abdominal mus- 
eles. Naturally, the amount of muscular 
force so expended is still suited to the re- 
quirements of the denser air to which one 
has been accustomed. As the atmospheric 
pressure is diminished, the air escapes more 
rapidly and the expected sound is not 
formed. In order to learn again how to 
whistle, it is necessary to place the lips in 
another position and to apply the muscular 
force differently, which always requires 
considerable time and practice. 
Physicians who have made a short stay 
at Davos, which lies at an altitude of only 
1,600 meters (5,200 feet), state that during 
that time their respiration was much ac- 
celerated, while there was an inability to 
breathe deeply. The explanation of this 
phenomenon is the diminished atmos- 
pherie pressure which also causes an ac- 
celeration of the pulse-beats—the inevit- 
able result of insufficient lung-expansion. 
Accelerated breathing at high altitudes 
affects metabolism by aiding in the re- 
moval of gaseous excretions, such as carbon 
dioxide. 
Aéronauts observed the acceleration of 
the pulse to be the first physiological 
change. They can reach a much higher 
altitude than mountain climbers without 
having any difficulty in sustaining respira- 
tion, as their muscular exertion is not so 
great. Butthe transition to the rarefied 
air is more sudden, and the increased, 
‘difficulty in breathing, which now appears 
although the aéronaut is generally uncon- 
scious of it at first, results from an insuffi 
cient expansion of the respiratory organs, 
which renders them incapable of admitting 
the requisite amount of rarefied oxygen 
The strength of his respiratory muscles is 
diminished; he finally loses control of his 
limbs, and his senses are dulled. This 
