28 
F. S. BILLINGS. 
of the lungs is equal. The falling together of the lungs on open¬ 
ing the thorax is also the consequence of retraction, the elasticity 
of the lungs exerting an equal influence with the external atmos¬ 
pheric pressure. We know that expiration results without the 
employment of muscular force; it results from the endeavor of 
the ribs to return to their state of a quiescence, though the pres¬ 
sure executed by the intestines which pushes the diaphragma 
forwards, through the relaxation of the inspiration muscles, and 
from the endeavor of the elastic lungs to make themselves smaller. 
Muscular force is only exerted by forced expirations in order to 
contract the thorax, the intestines are thereby compressed, the 
diaphragma pushed forwards, the ribs drawn forward. The 
lungs of dead animals represent a condition of expiration which 
is not forced. This state of expiration corresponds to that grade 
of retraction which is possible by an intact thorax. 
With the opening of the thorax is produced that equilibrium 
between the internal and external atmospheric pressure which we 
have previously considered; hereby the elasticity of the lungs 
becomes again active and causes a full retraction of the same. 
The lungs, when removed from the cadaver, exemplify this condi¬ 
tion, on condition that they are elastic, and the respiratory tube 
is not obstructed. Both are stadia of the same mechanical pro* 
cess; in both the lungs still contain air. We must also distinguish 
between atelectasis and a full condition of retraction. This latter 
condition is caused by the equal distribution of the intra and 
extra pulmonic atmospheric pressure. If I decrease or remove the 
intra pulmonic atmospheric pressure, I then make it possible for 
a further retraction of the tissues of the lungs, which may finally 
produce atelectasis. Atelectasis is then the retraction of the pul¬ 
monic tissues until they contain no more air. The process upon 
the lungs is not a pathological one, it is a known physiological 
act, which has only appeared in an abnormal grade. Not the pro¬ 
cess, but the grade of the same is pathological. 
What is then compression of the lungs ? 
The lungs or parts of the same may be compressed intra vitam 
by water, blood, fibrin, pus, tumors, etc. The fluid cet. par. 
assumes the lowest part of the thorax, therefore the lowest parts 
