It seems therefore that it might be said that the move-
ment of balance of the diaphra.gm may be observed in spite

* Barjon examined, through courtesy of Dr. Dumarest, a series of fourteen
cases of pneumothorax at the Mangini Sanatorium. All these cases had
positive pressure; the balance movement, however, was foimd in only one-
half the cases. The case which had at the same time the balance movement
and the pendulum movement most marked, had only a meditmi pressure of
+ 4.
With P. Counnont, Barjon saw a splendid balance movement in a woman
where pressure reached only — 6+2 and in forced inspiration fell to — 6
+ 0.
PNEUMOTHORAX 67

of a slight effusion, but a large effusion rather prevents it
from being produced.
Does the pressure signify anything? What role has it
in the production of the phenomenon?

The r61e of pressure has a certain value, but it does not
act except when combined with other necessary conditions;
it is not even necessary that the pressure be very high. A
pressure although very high is not sufficient alone to stimu-
late the paradoxical movement of the diaphragm if the
other conditions are not fulfilled.
The mechanism of the movement of balance appears
therefore as rather complex and this would explain its rela-
tive rarity in pneumothorax. It is often lacking, in fact,
and Bar j on estimates that it is only met with in about 40
out of 100 cases.
This phenomenon would seem to result from a kind of
unstable equilibrium established on both sides of an inert
floating membrane, very sensitive to the slightest varia-
tions — the diaphragm in this particular case.
