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in relation to the genesis of cardiac dilatation. It is conceivable that a marked constriction of
the pulmonary arterioles and an increased resistance in the lung might, by greatly raising the
pressure in the pulmonary artery, embarrass the action of the right ventricle, and lead to its
becoming distended,—a change that would be followed, secondarily, by a distension of the right
auricle. But in such a condition the left side of the heart would not be dilated, but rather
collapsed. Now, we have seen that the whole organ becomes dilated
—the left side as well as
the right—and consequently the above hypothesis of increased pulmonary resistance—even if
there was any proof of its occurrence
—is entirely inadequate.
It is clear, from what has been stated that the occurrence of dilatation is not dependent
on changes in the systemic blood-pressure (though usually associated with such changes), nor
yet upon changes in the pulmonary circuit: it is due to some influence exercised by chloroform,
either directly on the heart itself or indirectly through the cardio-inhibitory centre in the
medulla oblongata and the vagus nerves. The influence of the cardio-inhibitory centre can
readi l y be excl uded by secti on of the vagi I have frequentl y cut those nerves, and then repeated
the administration of chloroform, with the result that the heart became dilated as before.
Moreover, the same happens after the injection of atropine in sufficient amount to paralyse the
inhibitory function of the vagus. Hence it is evident that the dilating influence of chloroform
is exerted, not through the vagus nerves, but directly on the heart itself. Chloroform
acts upon the heart; it causes a marked depression of cardiac muscle involving a reduction of
its tone relaxation of the cardiac walls, and an impairment of their functional efficienc
y .
P e r i o d i c D e p r e s s i o n o f t h e V e n t r i c u l a r A c t i v i t y
after Chloroform
—In some animals
a peculiar result was observed some time after a dose of chloroform had been given. The
sequence of events, as shown by the graphic records, is as follows: A dose of chloroform (1 to 2
minims) was injected into the bottle, and led to a more or less marked fall of the blood-press
ure and a certain amount of cardiac dilatation. These results gradually passed away, the blood-
pressure rose, and the heart resumed its ordinary condition. But, while the blood-pressure was
rising and the cardiac condition improving, or even after the blood-pressure and the heart
had recovered, there sometimes suddenly developed a remarkable change in the ventricular
action. The force of the beats became greatly diminished, the ventricles were imperfectly
emptied, and they became more or less markedly distended with blood. The curves inscribed
by the ventricular beats upon the smoked surface were much reduced in height, and the base
line or general level of the tracing was markedly elevated for a time. This condition was
soon more or less completely recovered from; but it sometimes recurred again and again in a
ver y r emar kabl e f as hi on. I n s ome i ns t ances t hi s cur i ous per i odi c ef f ect on t heventricles was
seen to follow the administration of very small doses of chloroform, which had only compara-
tively slight primary effect on the blood-pressure and the heart. The auricular action is not
affected proportionally to the ventricular chan
ge
—
indeed, it usually shows only a Very slight,
and gradual reduction.
Such a periodic depression of the ventricles had, in my experiments, always been
preceded by a dose of chloroform. It is probably due to a direct influence exercised
o n
the heart; it does not seem to be affected by section of the vagi. I have never seen any depres-