INFLUENCE OF THE BRAIN AND SPINAL CORD
201
same result on repeating this experiment. The experiments which
Bracket* and others have instituted on living animals, for the pur¬
pose of determining the irritability of the nerves, are of no value with
regard to the heart, its action being so much affected by painful
impressions.
Another phenomenon which distinguishes the heart from other
muscles is the persistence of its rhythmic contractions in thei^ regular
order in the different cavities, even when removed from the body
and emptied of its blood. This cannot be explained otherwise than
by supposing the heart under these circumstances to retain with its
nerves some specific nervous influence.t The influence of the nerves,
therefore, seems to be the ultimate cause of the contractions of the
heart; as the great effect which irritations of the brain and spinal
marrow, and passions of the mind, have in modifying its action also
tends to show. If it were possible to destroy the vital function of the
nerves, without at the same time depriving the muscles of their
power of contraction, this question might be set at rest; but unfor¬
tunately the narcotic agents, which, when applied to the nerves, take
from them their property—when irritated—of exciting contractions
in the muscles to which they are distributed, render the muscles in¬
capable of exercising their contractile power when the nerves are
irritated. Opium applied to the heart of a frog soon puts a stop to
its motion; this effect being produced, as Henry has shown, very
rapidly when the narcotic is brought into contact with the inner sur¬
face of the organ, but more slowly when it is applied merely to its
outer surface. It is evident, however, that the nerves have a great
share in the heart’s action, from the sudden disturbance and cessation
of the rhythmic movements when the whole spinal marrow is sud¬
denly destroyed.
Influence of the brain and spinal cordon the hear Vs action.—
The inquiry respecting the part of the nervous system whence this
influence on the heart is derived, whether from the cardiac nerves
and sympathetic system, or through the medium of these from the
spinal marrow and brain, was originated by Bichat. Before entering
into this inquiry, it will be necessary to give a sketch of the principal
divisions of the nervous system. The functions of the two systems
of nerves were more exactly defined by Bichat. The nerves arising
from [connected with] the brain and spinal marrow have, for the
most part, the power of exciting voluntary motion in the muscles to
which they are distributed, but lose this power when their connec¬
tion with the nervous centres is cut off; and the nerves arising from
the spinal marrow are also deprived of the power of communicating
* Recherches sur le système ganglionaire.
t Remak (Casper’s Wochenschrift, No. X. 1839) states, that the minute
branches of nerves which he had traced into the muscular substance of the heart
in man, as well as in many mammiferous animals, consist like other parts of the
sympathetic nerve of the peculiar gray organic nervous fibres beset with small
ganglia (see the fourth chapter of the second section in the book on the Nervqus
System). And by the presence of these numerous ganglia, or centres, of nervous
influence, he explains the continuance of motion in the „heart after its separation
from the body. But it must be remarked, that Valentin denies the existence of
these gangliated organic fibres.