November 2, 1874.]

LECTUEES OH THE VASCULO-CAEDIACS.?BT A. CEOMBIE.

ORIGINAL COMMUNICATIONS.

endo-cardiac blood-pressure, the systemic vessels pressure lowered, and the heart relieved.

LECTURES ON THE VASCULO-CARDIACS.

mogastric

Ill other animals this

Officiating

By Alexander Crombie, M.D., Edin., Professor of Materia Medica and Clinical Medicine, Medical College, Calcutta.

LECTURE II.?DIGITALIS (continued.) ACTION (Thb

OX THE

HEART.

rhythmical action of the heart is not quite clearly understood. It is due to an inherent vital property either of the muscular fibres themselves, or what is more probable, of the intra-cardiac ganglia of Remak, for the apical portion of the ventricle of the frog ceases to act rhythmically when divided from the still beating basal portion, which contains numerous ganglia, while they have not been found in the apex. The action of the heart is quickened when the sympathetic cardiac nerves are stimulated. These nerves convey, from the medulla oblongata to the cardiac organ, influences which accelerate its action. They pass from the medulla through the cervical portion of the spinal cord to the Middle and inferior cervical ganglia, and thence to the heart, where there is every reason to believe they terminate in the intra-cardiac ganglia. On account of this its function, the root which connects the inferior cervical ganglion in the rabbit with the spinal cord is called the nervus cause

of the

^celerana.

(ralbit). of the heart of the Diagram the innervation Diagram of innervation of the heart (rabbit).

and

There is

nerve

is

more or

are

281

dilated,

the blood,

less bound up with the pneu-

sympathetic trunks.

a general concurrence amongst observers that digitalis and digitalin on the action of the heart is first a slowing of its contractions, then an acceleration, and finally again a slowing, terminating in arrest of its action if the dose be a sufficiently large one; and if the heart of a frog be exposed and watched while under the isfluence of the drug, digitalin will be seen to increase the contractility of its muscular fibres at first, then to render their contractions irregulars and finally to confer upon them a peculiar rigidity. Along with these phenomena is observed the increased blood-pressure in the arteries, which we have already considered, and which persists during the first and second stages of the effect on the heart, but gives way to diminution in the blood-pressure in the last stage when the heart's contractions again become slow and are irregular. 1. We will consider first the stage of primary slowing. Is this slowing due to a direct action of digitalis on the muscular fibres of the heart, or on the numerous ganglia situated in its substancc, but chiefly in the neighbourhood of the auriculo-ventricular openings ? Is it due to an action on the accelerator" nerves which pass to it through the lower cervical ganglia, or to direct stimulation of the pneumogastrics whose now

the effect of

"

function it is to slow the heart's action ;

or

is it

results of the increased tension in the arterial

one

system,

of the which

already considered ? That it is partly at least the result of excitation of the vagus there seems to be no doubt; but this excitation may be caused either by a direct stimulation of the vagus as one of the actions of digitalis, or it may be caused by the stimulation of the vagus we

SIC

have

of the increased pressure of blood as the consequence within the cranium, or partly also of the increased endo-cardial pressure on the vagus-ends in the heart itself. The proof that it does take place through the vagus is an exceedingly beautiful and ingenious one. You know that if the peripheral end of the centre

divided vngus be stimulated

by electricity,

the heart is at first

slowed, and if the stimulation be sufficiently powerful it will

the heart; M, medulla oblongata; SC, spinal cord; S, symoetic; V, vagus; si, superior laryngeal; ec, superior cardiac; il,

laryngeal; ic, inferior cardiac jn(j.r'or cate the directions in which the

branches of vagus. currents travel.

nerve

nerve-cells an'SIil

are

represented

as

The

arrows

Two intra-

forming, with their fibres,

a

reflex

whereby the rhythmical action of the heart is probably '"arily carried on.?Modified from Rutherford's Lectures on Exp. Phys.

orcT