t*.

ly

•M'

/

[From the journal of Physiology.

I

Vol IV. No. 2.]

ON THE INNERVATION OF THE HEART, WITH
ESPECIAL REFERENCE TO THE HEART OF
THE TORTOISE. By W. H. GASKELL, M.D., F.R.S.
[Plates II— V.]

[From the Physiological Laboratory, Cambridge.]

The views held by physiologists upon many points connected with
the innervation of the heart have been too exclusively based upon
observations upon a single type of heart, viz. that of the frog. It is
therefore very advisable wherever possible to control these experiments
by a corresponding elaborate series of observations upon the hearts of a
large number of other animal types, and in this way to trace the
evolution of function in the same way as the morphologist tracks that
of structure. With this object in view I propose in this paper to
discuss as fully as I can the series of experiments which I have made
during this last year upon the innervation of the tortoise heart,
comparing them at the same time with corresponding observations
upon the hearts of other animals. I shall therefore embody in this
paper the substance of three separate preliminary papers which I have
already published, viz. :

1. Preliminary observations on the innervation of the heart of the tor-
toise\ 2. On the sequence of the contractions of the separate parts of
the heart^. 3. On certain points in the function of the cardiac muscle®.

I propose to divide the paper into four parts, viz. :

1. On the spontaneous rhythm of the different parts of the heart
and of the heart as a whole ;

2. On the sequence of the contractions of the different heart
cavities ;

3. On the action of the cardiac nerves ;

4. On the action of atropin and muscarin ;

and in each part to strictly confine myself to the subject matter of that
part.

In a concluding section a general discussion on the four previous
sections will be given.

* Journ. of Physiology, Vol. ui. Nos. 5 and 6.

Brit. Med. Journ. 1882, p. 672.

^ Proc. Camb. Phil. Soc., Vol. iv., Pt. v.

f .. J .

u •

-*

PH. IV.

0

44

W. II. GA8KELL.

PART I.

On the spontaneous rhythm of the different parts of the heart
and of the heart as a whole.

In the early days of physiology before the nerves of the heart were
known or ganglion cells thought of, the beat of the heart was attributed
to the direct stinaulating action of the blood upon the cardiac muscle.
The discovery of the cardiac ganglia and especially their situation in
that part of the heart — the sinus — from which it had been long recognised
that the rhythmical beat took its origin; led instantly to the hypothesis
that they played the chief part in the causation of the beat, although
at the same time they were recognized as appendages to the nerves and
not as separate independent structures. The fact that upon section
certain portions of the frog’s heart continued to beat while other portions
remained quiescent and that ganglion cells were always found in the
former seemed proof positive of their preponderating influence in the
causation of rhythm. Further, the knowledge that the respiratory
muscles responded to rhythmical discharges sent out from the nerve
cells of the respiratory centre naturally led to the conclusion that the
supposed motor nerve cells of the sinus of the heart caused the heart’s
beat by a series of separate single discharges, each of which brought
about a contraction- of the cardiac muscle. When however from the
experiments of Eckhard, Foster, Merunowicz and others it was
known that a constant stimulus whether electrical, chemical or mechanical
applied to the muscular tissue of the apex was able to cause that muscle
to beat rhythmically even although no nerve cells were to be found in
it, the question arose — Are reaUy these motor centres similar to those
of the resph’atory centre, or is it not more likely that they supply a
constant stimulus to the muscle and that it is the property of the
cardiac muscle to produce a rhythmical result from that continually
acting stimulation ? Whichever view be accepted we still see that
certain ganglia are supposed to possess motor functions upon which the
heart-beat ultimately depends, and the cardiac muscle itself is not
supposed to possess any power of automatic rhythm but merely contracts
rhythmically upon the application of a suitable external stimulus.

Further the experiments of Stannius have given rise to many
investigations and much discussion upon the question, whether the
automatic rhythmical power is confined to the region of the sinus or is

INNERVATION OF THE HEART.

45

inherent in other portions of the heart of the frog ; whether, therefore,
the rhythm which is observed after removal of the sinus and other parts
is in reality automatic, i. e. produced by internal causes in the rhythm-
producing tissue itself, apart from external stimuli, or whether it is due
to some stimulus caused by the operation itself. We may briefly sum
up the main facts which have been accumulated on this question as
follows : —

1. Kemoval of the sinus by section or ligature causes a temporary
standstill of the auricles and ventricle followed by an auriculo- ventricular
rhythm, which is at first slow and though gradually quickening, never or
seldom reaches the rate of the sinus rhythm.

2. The duration of this standstill depends upon the situation of the
section, being very slight or even absent when the section is made
exactly at the junction of the sinus and auricles, and much greater when
a portion of the auricles is cut away as well as the sinus.

3. During the standstill removal of sinus and auricles by section or
ligatirre in the auriculo-ventricular groove causes a rhythm in the
ventricle, which is quickest immediately after section and then gradually
becomes slower and slower up to complete and permanent standstill of
the ventricle.

The rhythm of the ventricle described in § 3 is clearly from the
nature of it a rhythm of excitation and not automatic; the fact
that the greatest rhythmical effect is produced immediately after the
operation and gradually dies away shows clearly its dependence upon
the method of procedure, as well as the difference between its causation
and such a rhythm as is seen after the first Stannius ligature, where the
contractions commence with long intervals between them and gradually
quicken in rate. In addition, as I have shown in my paper read before
the Royal Society* Dec. 1881, it is possible, by properly applying a
micrometer screw clamp to the auriculo-ventricular groove, to separate
the ventricle from the sinus and auricles without producing any in-
dependent ventricular rhythm whatever. I found that if the clamp be
tightened suddenly and forcibly, an independent ventricular rhythm was
set up, often lasting a long time, but always becoming slower and slower
and finally ceasing ; but that if the clamp be tightened gradually a short
series of independent ventricular beats might occur with each move-
ment of the screw exactly similar to those often seen in the amide and
ventricle, before the standstill takes place, when the sinus is removed by

1 Phil. Tram., Part iii., 1882.

5—2

46

F. II. 0 ASK ELL.

section, ligature or clamping at or near the sino-auricular groove. In
other cases I have succeeded in isolating the ventricle without causing
any independent ventricular contractions.

We may then leave out of consideration the contractions which are
evidently due to the stimulus caused by the operation and shall therefore
an’ive at the following law : —

“The power of independent rhythmical contraction de-
creases regularly as we pass from the sinus to the ventricle.”

YI& can however go further; for although the ventricle remains
permanently still after separation and therefore does not appear to
possess automatic rhythmical power, yet a very slight amount of
assistance is required to set it in rhythmical action; the presence of
a blood solution in its cavity, together with a slight amount of internal
pressure is sufficient to bring to view its latent rhythmical power, to
produce in it a permanent rhythm which is not at its maximum rate
when the blood first passes through, but on the contrary does not
commence for some little time and then beginning at a slow rate
quickens to a more or less regular rhythm. So too the apex itself can
be set in rhythmical action with however greater . difficulty than the
whole ventricle ; the standstill after the blood begins to pass in is here
much longer, the production of any rhythm at all is much less certain
and the rhythm itself is slower and less regular.

We see then that the part of the ventricle which is nearest the sinus,
viz. the base, is nearer the condition requisite for the manifestation of
automatism, than the part further removed, viz. the apex; and in
accordance with this, we know that a slight stimulus applied to the
base of the ventricle will cause a series of ventricular contractions, while
the same stimulus applied to the apex will cause only a single contraction.

If therefore we use the term “rhythmical power” to represent the
capability of rhythmical contraction in any heart segment, whether that
rhythm be strictly automatic or requires external assistance for its
production, we can say that —

“The rhythmical power of each segment of the heart varies
inversely as its distance from the sinus.”

It may be urged from experiments upon the frog alone, that the
rhythm of the isolated ventricle or apex is fundamentally different from
that of the isolated auricles, in that the latter is so much more clearly
automatic than the former; that therefore these two kinds of rliji-hm
have in all probability a different origm, the former being essentially
due tp the properties of the muscular tissue and constituting a

INNERVATION OF THE HEART.

47

purely muscular rhjrthm, while the latter resembles that of the heart
as a whole and depends for its production upon the rh}rthmical qualities
of some nervous mechanism presumably of the nature of motor ganglia.
Whether there is any fundamental difference in the rhythmical properties
exhibited by the sinus, by the auricles, the ventricle, and the apex of
such a character as to necessitate the hypothesis of two distinct modes
of origin, the one nervous and the other muscular, can be better decided
when we have compared the behaviour of the heart of the tortoise in
this respect with that of the frog.

All experiments involving the removal of the different ganglionic
masses or section of the large intra-cardiac nerve trunks can be per-
formed on the tortoise with much greater ease and certainty than on the
frog; for, in the former the nerve trunks with their accompanying
ganglia are situated externally lying in or just under the visceral
pericardium, the septum between the auricles containing neither nerves
nor blood-vessels ; while in the latter as is well known the nerves run
internally along the septum between the auricles. The septum then in
the tortoise has no such importance as in the frog. Its place is taken
by a flat band of tissue which connects the sinus and ventricle, from
which on each side the two auricles spring. This band is plainly visible
if the heart be turned over by seizing the apex of the ventricle as is
represented in the accompanying woodcut (Fig. 20). It is seen as a

2p. Ventricle turned over, to show the connection of the sinus (S) by means of
the junction wall (J) with the ventricle (V) and. the auricles (A). The point of a seeker
18 placed under the free coronary vein and nerve (C).

48

W. H. GASKELL.

band of tissue joining together the two auricles but differing in ap-
pearance from the rest of the auricles. This junction wall (J) of the
auricles is flat and smooth, not bulged out like the rest of the auricular
tissue, and the two auricles (A) spring from it as from a flat base, like
fungi groAving on a flat strijD of wood. The septum between the auricles
arises from the central line of this junction wall. The two vagus nerves
pass to the sinus with the sup. venae cavae and their main trunks pass
from the sinus to the auriculo-ventricular junction just under the peri-
cai’dium covering this junction wall, so that this band of tissue which not
only joins together the two auricles (A), but connects the sinus (S) with
the ventricle (V) is of the same physiological importance that the septum
is in the frog.

In my former paper ‘ I have described fully the method used by me
in investigating the nature of the rhythm of the heart and the action of
the cardiac nerves in the frog and toad. This method enables slight
variations in the force of the contractions of both auricles and ventricle
to be simultaneously registered as accurately as has hitherto been
accomplished for the rhythm alone. Its principle consists in the fixing
of a point of the heart and registering the contractions of any two
parts which are separated by that fixed point, the recording being
effected by means of two levers attached by silk threads to the two
parts of the heart thus separated. Such a method can be applied to
the hearts of all animals whether in the body or out of the body ; and
as soon as the first experiments made on the heart of the frog in
January and February 1881 convinced me of the great value of the
method, I determined to examine in the same manner the nature of the
heart beat and the action of the cardiac nerves in the first instance in
the case of all available cold-blooded animals and finally to pass on to
the heart of the warm-blooded animals ; being convinced that the study
of the evolution of function as we pass up higher in the scale of animal
developinent is the true method by which the complex problems of
the mammalian heart mil receive their final solution. Such a task
necessarily demands a large amount of time, especially when, as I have
seen in the course of the last year, the investigation of each new animal
introduces new variations, and thus suggests new problems to be solved.
It is therefore with pleasure that I find that Dr Roy has undertaken the
investigation of the action of the vagus and accelerans nerves upon the

^ Phil, Trans., Part iii., 1882.

“ Proc. Camb. Phil. Soc., Vol. iv., Pt. ii., p. 76; read March 7, 1881.

INNERVATION OF THE HEART.

49

heart of the dog by a method which is the same as that which I have
used for the frog and the tortoise. This method gives results for the
mammalian heart which are as striking as those seen in the case of
the frog and the tortoise.

In the majority of my experiments on the frog and toad, I made use
of a clamp to fix the heart in position. In the tortoise it is more con-
venient simply to hold the aortic trunk when it is desired to register the
contractions of the auricle and ventricle ; I have therefore made use of
the clamp chiefly in the sino-auricular groove in order to register
separately the contractions of the sinus and auricle. My method of
experimentation is as follows : — The heart is removed together with the
upper portion of the body of the tortoise, the pericardium slit open and
the liver carefully cut away ; the aortic trunk is cut across and held by
a pair of Kronecker’s forceps, a silk ligature with a hook at one end is
tied to the very apex of the ventricle and another to the top of the right
auricle, and the vagus nerves are exposed in the neckj^atured and cut.
The whole of the upper portion of the body is now^^ced on a stand
and fixed in a suitable position between the two levers. The small
forceps attached to the aorta is tightly held by an ordinary holder and
the two hooks are attached to the upper and lower levers respectively.
The appearance of the heart is given in the accompanying woodcut
(Fig. 21), which shows at a glance the position of the sinus, auricle and

50

W. H. GA8KELL.

ventricle without further description. In most of the experimertts which
I have made on the tortoise heart I have not used a clamp in order to
hold the heart firm but have simply held the aorta in a suitable holder,
so that in these cases any separation of the different parts of the heart
is made by section and not by clamping.

The consideration of the large number of experiments at my disposal
brings out certain differences between the frog and the tortoise. In the
first place, the ventricle of the tortoise when isolated beats automatically
^vith as great a certainty as the isolated auricle. The extra assistance
in the shape of some constant chemical, mechanical or electrical stimulus
which is required by the frog’s ventricle to make it beat rhythmically is
not needed here ; the rhythmical p^ower of the ventricle of the tortoise
as a whole is greater than that of the frog and is of identically the same
nature as that of the auricle. In the tortoise then we can compare
strictly the rhythm obtained from the ventricle with that of the auricles
and sinus, and see whether there is the slightest reason for attributing
different origins to them, for ascribing the former to the properties
of the muscular tissue and the latter to those of the nervous elements.

First then I will compare the resemblances and differences between
the resulting rhythms, when the separation has been effected either by
clamping or section, at the junctions of the sinus with the auricles, and of
the auricles with the ventricle. In both cases the production of the
automatic rhythm presents the same characteristics, viz., the beats are
at first slow and gradually quicken to a greater and greater extent ; in
both cases a longer or shorter time may elapse before an independent
beat takes place, or a rhythm of excitation may be caused, characterized
by contractions which, at first quick, gradually slow down and give place
to and merge into the slowly commencing automatic rhythm. The
differences are differences of degree not of kind, and can be summed up
by saying that the rhythmical properties of the auricles are more
easily developed than those of the ventricle ; thus, (1) when the inde-
pendent rhythm starts its rate is much slower in the ventricle than in
the auricle ; (2) the auricular rate can increase up to or near to that of
the sinus more easily than can the ventricular ; (3) a perfectly regular
rate is reached more quickly by the auricle than the ventricle. The
preliminary pause, which after separation often takes place before inde-
pendent contractions begin, is either absent or very short when the
simis is removed by section or clamping exactly at the junction of the
sinus and auricles, and is well marked when the section is made between
the sinus and the ventricle or in the auriculo-ventricular groove, pro-

INNERVATION OF THE HEART.

51

vided that in this latter case a rhj^thm of excitation is not set up by the
clamp or the section sufficient to obscure the standstill. In Figs. 1, 2,
PI. II., I give examples of the development of rhythm when both auricle
and ventricle are left and also when the ventricle alone remains. The
close relationship between the automatic rhythm of the ventricle and of
the auricle is further shown when the section is made between sinus and
ventricle ; the rhythm which then occurs resembles in its characteristics
sometimes that of the ventricle sometimes that of the auricle, though
perhaps on the whole, as long as any part of the junction wall between
the two auricles is left in connection with the ventricle, the resulting
rhythm tends rather towards the auricular than the ventricular type.
The evidence then shows strongly that the automatic rhythm of the
ventricle is of the same kind as that of the auricle, and therefore as that
of the sinus, so that if the latter is due to the presence of motor ganglia
so too is the former, and on the other hand, if the former be due to some
inherent rhythmical property of the ventricular muscle then the latter is
due to a somewhat better development of the same kind of property in
the muscular tissue of the sinus. The possibility of deciding between
these two views is given by the study of the rhythmical power of the
ventricular muscle freed entirely from ganglion cells; in other words,
by the comparison of the rhythmical power of the muscular tissue from
the apex of the ventricle with that of the whole ventricle.

My method of experimentation is as follows. A strip of muscular
tissue is cut from the apex of the ventricle in the direction and of the
size represented by the dotted line in Fig. 20, p. 47, and held firmly at
one end ; a thread of silk is tied to the free end and attached by means
of a hook to the lever of an ordinary muscle and nerve moist chamber.
A very thin we, insulated except at the ends, is twisted round each
extremity of the strip of muscle and connected by means of a Du Bois
Reymond key with the secondary coil of an ordinary induction apparatus.
By means of this induction coil an interrupted current can be sent
through the whole strip of muscle, and owing to the extreme ^^mness
of the two wire electrodes the muscular strip can register an^ move-
ments without the slightest impediment. At the fixed end of the
muscular strip, so as to touch the muscle on opposite sides, are placed
a pair of electrodes connected with another induction coil so arranged
as to send single induction shocks' into the muscle every ten seconds.
The muscular strip is moistened with the blood of the animal or a drop

1 N.B. Throughout this paper a single induetion shoek ineludes both the making and
breaking shook. ^

52

W. II. GASKELL.

of salt solution, wet blotting-paper is placed in the moist chamber, the
glass cover is put in position, and the experiment can then commence.
The experiment consists in causing rhythmical contractions of the
muscular strip every ten seconds by means of the single induction shocks
applied at one end, and at the same time observing at intervals the
effect upon these contractions of sending through the whole strip an
interrupted current so weak as not in itself to cause contractions. The
single induction shocks are of such a strength as to be certain of causing
a contraction each time. The sequence of events is as follows — When
the artificial rhythm is first induced the contractions are small, irregular
in size, and somewhat flat-topped. Upon inspection it can be seen that
a number of blocks exist in the strip of muscle (see p. 66, and Fig. 3,
PI. II.), so that the contraction started at the fixed end passes a short dis-
tance only along one region, while at another part the contraction though
delayed eventually passes on, and at still another part it is perhaps only
every second contraction which passes ; and so on. It is in this way that
the weak irregular contractions are caused, and the first effect of the ap-
plication of the interrupted current is to remove these blocks. Each time
the interrupted current is sent through, the contraction due to the single
shock is enabled to pass a little farther; gradually and surely all the
blocks are removed, the contractions become more regular in force,
stronger, the passage of the contraction becomes more rapid until at
last the strip contracts evenly and vigorously from end to end ; every
obstruction is gone, the conduction power and contraction force is fully
restored. The excitability of the tissue gradually increases hand in
hand with the restoration of contraction power; the single induction
shocks do not require to be so strong in order to cause an invariable
contraction, the interrupted current must be made weaker in order not
of itself to cause contractions ; in fact the functional activity of the
tissue has been in every respect repaired and increased. Further, when
this process of repair has reached its maximum, when every induction
shocU.t^oduces equally strong vigorous contractions which pass rajjidly
and w^hout hindrance from one end of the strip to the other, then
spontaneous contractions begin to appear : the artificial stimulation can
be removed and the automatic contractions of the strqj of muscle be
observed. These independent contractions are as strong as those caused
by the single induction shocks ; they, like the automatic contractions
of the ventricle or of the auricle, commence with a slow rate of rhythm
which gradually and steadily quickens, becoming more and more regular
and approaching nearer and nearer to the rate of the sinus rhythm.

INNERVATION OF THE HEART.

53

Hour after hour the strip of tissue continues beating with unimpaired
vigour -ivith the same rapid regular rhythm ; kept in the moist chamber
through the night it is found to be still beating strongly and regularly
though more slowly on the next morning. How long this rhythmical
power remains, how long these vigorous contractions will continue
I cannot say; I have seen the strip beating with great vigour and
regularity as long as 30 hours after suspension, i.e. between 28 and 29
hours after the commencement of the spontaneous independent con-
tractions.

These contractions are clearly both myogonic and automatic.

They are myogonic because no special nerve structures are to be
found here, and when the rhythm is once well established the strip can
be cut into small pieces, each of which will still continue its rhythm for
a long time; the rhythmical power then is not specialized in any
portion of the strip, but is distributed over the whole of it. Its origin
must therefore be in the muscle or in the nerve fibres suppl3dng the
muscle, as is suggested by Schiff^ in his discussion on the mode of the
movements of the heart. That the rhythm is not only muscular in
origin, but also due to some quality inherent in the muscle itself, i.e. is
automatic, is clearly shown by the method of its development. It is
evidently not a “ rhythm of excitation ” due to the direct stimulation
of the muscle by the single induction shocks or the interrupted current,
for it continues at least 30 hours after the discontinuance
of all stimulation; it begins, like the automatic rhythm of the
ventricle and auricle, and unlike the excitation rhythm caused by the
second Stannius ligature, with contractions at long intervals from each
other, and then gradually and regularly quickens up to its maximum rate.
Further, nothing can be more striking than the nature of its develop-
ment; the gradual recovery of the conduction power throughout the
strip, the steady improvement in the force and rapidity of the con-
tractions, the increase of excitability, all show a gradual improvement
and development in the activity of the processes upon which the various
properties of the muscle depend, a development which when it rlfaches
its culminating point is manifested by the outburst of auto-
matic rhythmical contractions. In fact under the guidance of
the interrupted current and the single induction shocks the rhythmical
power inherent in the muscular strip has been developed and made
manifest, the muscle has been taught to beat.

1 Modus der Herzhewegung, Bosor’s Archiv, 1850, Vol. ix., p. 22 and 220.

1

54 W. II. GASKELL.

The action of the interrupted current is not absolutely necessary for
the manifestation of this rhythmical power, it simply hastens on the (

development of the automatic rhythm but does not produce any new |

property in the tissue. Thus if two strips of muscle be cut from the j

apex of exactly the same length and in every respect as similar to each |

other as possible, and the one strip be taught to beat in the manner j

described, while the other is simply left suspended in a moist chamber, I

without the application of any stimulus or any foreign fluid, then it is ]

found that after a time this latter strip is beating of its own accord, and j

beating with contractions which in most cases become eventually' nearly '

if not quite as strong and vigorous as those of the former strip. The ;

difference then between the behaviour of the two strips is in no way
essential, the same processes are taking place in the one as in the other,
but not at the same rate. Not only is the rapidity of the genesis of the 1

automatic rhythm markedly quickened, but also the rhythm itself is
more regular and quicker in the strip which has been taught than '

in the one which has been left alone. Thus in the former case I have
generally noticed the occurrence of independent contractions between i

one and two hours after the suspension of the strip ; in the latter I have j

never seen any sign of a beat under three hours, and seldom before four
hours after suspension. In the latter case as well as in the former the strip fj

continues to beat all night and is beating strongly, and well next morn- i |

ing, and indeed may be beating more regularly than during the previous
afternoon. Thus in one case where the rhythm of the control strip
was during the afternoon of Nov. 8th irregular, with a strong tendency j'

to the formation of groups, separated by single contractions at long f

intervals or by long pauses of 3, 7 or even 18 minutes duration, the i

rhythm when seen next morning (24|- hours after suspension) was f

perfectly regular at the rate of one beat every 25 seconds ; in addition r

the contractions were nearly as strong as on the previous day*. In ||

order to show the manner in which the rhythmical power of the tissue |

is gra(^ally developed I will endeavour to describe fuUy a typical case. «

Nov. 7, 1882. Plate II. Fig. 3. Curves i — vi. |

A strip of muscle, cut from the apex of the tortoise ventricle, was sus- i

pended at 3.30 p.m., and moistened, the electrodes being arranged as above

' I have never yet been able to obtain similar automatic contractions from- a strip
of muscle cut from the apex of the ventricle of the frog. In order to obtain success with
the strip from the tortoise ventricle it is adrisable that the animal be well fed, in a lively
vigorous condition, and therefore that the experiment be made during or at the end of the
warm months of the year.

1

INNERVATION OF THE HEART.

5a

described. Single induction shocks sent in at the fixed end every 10 seconds.
Weak interrupted current sent through the strip at intervals as marked in the
figures on the upper line. The first two curves represented in Fig. 3, PI. II.
show the original weak partial contractions of the strip in response to each
induction shock, the gradual improvement of the contractions, the removal
of blocks in the strip so that at first every second contraction was enabled to
pass a block, and then on again stimulating every contraction passed' (see
curve ii), until at last each contraction was of the same strength and had
nearly reached its full vigour. The same process continued, the contractions
became • stronger and stronger, passed more and more rapidly along the strip
until at last about one hour after suspension a spontaneous contraction
appeared occasionally, in addition to the contractions caused by the single
induction shocks. These spontaneous contractions became more and more
frequent and upon then removing the single induction shocks the strip was
found to be beating of its own accord somewhat irregularly and with consider-
able rapidity. The contractions quickly improved in regularity and rapidity
and the two curves (iv, v.) were taken between 5.30 and 6 o’clock. The
rhythm was then, as is seen, very regular and as rapid as the sinus rhythm.
All wires and electrodes were then removed and the preparation placed under
a bell-jar with plenty of moisture and left through the night. At 9.15 p.m.
when the laboratory assistant left, i.e. nearly six hours after suspension and
five hours after the commencement of the spontaneous contractions the strip
was still beating strongly and regularly at the rate of ten beats per minute.
On the next morning, Nov. 8, I found the rhythmical contractions still con-
tinuing, and at 11 a.m. i.e. 18 hours after the commencement of spontaneous
contractions the tracing Fig. 3, curve vi. was taken. The strip was then cut
into three pieces which were placed on a glass slide and kept moist. Each of
these pieces continued to contract rhythmically and were observed to be still
rhythmically contracting up to 1 p.m. i. e. 22 hours after removal of the strip
from the ventricle. Further observation was then discontinued.

We see then that just as the whole ventricle of the tortoise when
isolated remains quiescent for . a short time and then begins to beat, so
too any strip of the ventricular muscle begins to beat spontaneously
after a longer standstill;, just as the rhythm of the whole ventricle
commences with a slow rate and gradually increases to its maximum, so
does the commencing slow rhythm of the apex strip gradually increase
in rate. No fundamental difference therefore exists between the
rhythmical phenomena in the two cases, no extra factor is required for
the production of the one rhythm rather than of the other ; the differ-

‘ These alternately weak and strong contractions are probably the same as noticed in
my previous paper in the case of the frog’s ventricle.

56

W. II. GASKELL.

ence is oue of degi-ee not of kind, being mainly, that the length of time
required before the rhythm is manifested is, as might be expected from
the greater severity of the section, greater in the one case than in the
other. A strip from the apex of the auricle behaves in a manner very
similar to that from the ventricle apex. Since therefore the purely
myogonic rhythm of the apex is closely related to that of the ventricle,
and therefore as has already been argued to that of the auricle, and
since no line of demarcation can be drawn between the rhythm of the
auricle and that of the sinus, the logical conclusion is that the rhythm
of the sinus and therefore of the whole heart depends upon the
rhythmical properties of the muscular tissue of the sinus, and not upon
any special rhythmical nervous apparatus.

According to Engelmann^ the myogonic origin of the automatic
pulsations of the bulbus of the frog’s heart, as well as of the contractions
of the apex under the influence of a su2Dply of blood, &c., is demonstrated
by the fact that in both cases the rhythm never reaches the rate of
those parts of the heart which contain motor nerve centres; a difference
which is in accordance with the law that the speciflc irritability of
muscle is much less than that of nerves or nerve centres. Accord-
ing to this view then we may hope to decide between the nature of
the origin of two spontaneous rhythms by an examination of the
rates of such rhythms, especially when as in the case of all my experi-
ments, the portions of cardiac tissue, whether ventricle, auricle, whole
heart or apex, were all suspended in the same manner, and all under the
same conditions. Before however a comjDarison can be made of the
rates of the different j)ortions of the heart, it is necessary to know the
rate at which the whole heart beats when taken out of the body and
suspended in the manner already described. The heart of the tortoise
beats in almost every case with the most perfect regularity, varying
in rate, apparently according to the time of year, from 10 to 20 beats
per minute. Thus the average rate of the beat of the whole heart
when i^rst suspended was as follows: February nearly 10 per min.,
March 10‘4 per min., Ajjril 12 per min.. May 16 jDer min., June and July
nearly 20 per min., Oct. and Nov. 13’5 per min. In this series the
averages for the first four months are taken from a much larger number
of experiments than for the last four ; moreover the animals were kept
under cover during November. We have already seen that the rate
of rhythm of the isolated auricle or ventricle increases progressively

* Pfliiger’s Archiv, Vol. xxix., p. 425.

INNERVATION OF THE HEART.

57

from a very slow rate to a very much quicker one ; hence we have
no right to assert that that rhythm cannot attain the rate of the
sinus unless the experiment has lasted so long that the maximum
rate has been attained. When the clamp is tightened in the sino-
auricular groove the decision is easy ; the rate of the independent
auricular rhythm is fairly quick at the very commencement, and in a
comparatively short time may quicken so as to reach the original sinus
rhythm. Thus the following examples show that there is no essential
difference between the sinus and whole auricle as far as rapidity of rate
is concerned.

Feb. 8, 1882. The clamp had been placed in the auriculo-ventricular
groove, tightened, and the development of the independent ventricular
rhythm observed ] the ventricle was then cut away, the auricle attached to
the lower lever, the sinus to the upper, and the clamp placed in the sino-
auricular groove. This clamp was then tightened and the auricle immediately
began to beat independently of the sinus, slowing down in the first ten beats
until the length of the pause between two consecutive .beats reached 14 secs,
and then gradually quickening until in between 9 and 10 minutes after
the separation the auricular contractions were as rapid and regular as
the original sinus contractions (the rate in each case being 1 in 4 ’6 secs.),
though absolutely independent of them and indeed the rate of these had
by this time quickened up to 1 in 3 '8 secs.

Dec. 20, 1882. In this case the sinus was cut away at the sino-auricular
groove and auricles and ventricle left suspended ; no standstill occurred but
the slow auricular beats improved in rapidity in a somewhat irregular
manner until in between 20 and 30 minutes after isolation the auricle and
ventricle were beating at a rate slightly less than 12 beats per minute, the
original sinus rate being slightly over 12 beats per minute.

When however the section is made or the clamp tightened between
the sinus and ventricle or in the auriculo-ventricular groove, then it is not
so evident that the ventricle has the power of initiating a rhythm equal
in rate to that of the sinus ; for the pauses between the beats are at
first so long and the increase in rate becomes soon so gradual that the
observation has to be discontinued before the maximum rate has been
attained. In the following example I give a typical case of the be-
haviour of the isolated ventricle during six hours’ continuous observation,
to show the manner in which the rate of the ventricle and the rate of
the sinus gradually approach each other, the one becoming slower and
slower, the other quicker and quicker.

58

W. H. G ASK ELL.

Feb. 9, 1882. Plato II. Fig. 2, curves i — vii. The heart was at 12
o’clock suspended with the auricle attached to the upper and the ventricle to
the lower lever, and was held by means of a clamp in the auriculo-ventricular
groove. This clamp was tightened to its uttermost so as to separate the
ventricle absolutely from the auricle and sinus j the preparation was moistened
at intervals and a series of tracings were taken up to 6.40 p.m. When the
clamp was tightened, a rhythm of excitation was set up in the ventricle
which gradually became slower and slower until it reached its minimum
as seen in curve i. No absolute standstill took place, but from this
minimum point the rate of the ventricular beats steadily improved as is
shown in curves ii. and iii. which were taken immediately in succession to
curveT. Curves iv., v., vi., vii. were taken at 2.45, 4.0, 5.15, and 6.40 p.m.
respectively, and are selected out of the whole number taken in this
experiment as fairly illustrative of the rate at which the rhythms of the
ventricle and of the sinus tended to approximate by the quickening of the
one and' the slowing of the other.

This experiment shows that the establishment of the full rhythmical
power of the isolated ventricle takes place very slowly when the ventri-
cle is simply kept moist but is otherwise not interfered with. If how-
ever it be supplied with suitable food material then the full rhythmical
power is manifested much more quickly, then the rate of rhythm easily
reaches that of the sinus.

The heart of the tortoise differs from that of the frog in the manner
of its blood supply ; for whereas in the frog a special system of blood
vessels does not exist for either ventricle or auricle, in the tortoise the
ventricle is supplied with a well developed coronary system which,
commencing as two fine arteries in the systemic aorta a little above the
aortic valves, ends in a number of coronary veins which pass from the
auriculo-ventricular groove to the venous sinus along the junction wall
of the two auricles. This coronary system is confined to the ventricle,
the auricular tissue like both auricle and ventricle in the frog being
entirely devoid of blood-vessels. If a cannula be tied into the
systernic aorta above the origin of the coronary arteries and a blood
solution he sent through it under a sufficient pressure, this pressure
will close the aortic valves and so prevent the blood passing into the
ventricle, while at the same time it sends the blood through the coro-
nary system and so into the venous sinus. If further the junction wall
between the auricles and therefore the coronary veins be cut across,
the blood which has passed through the thickness of the ventricular
tissue will drop from the cut ends of the veins instead of passing

INNERVATION OF THE HEART.

59

into the venous sinus, and so any distension of the heart cavities with
blood will be prevented. In this way then the muscular and nervous
elements of the ventricle can be supplied with blood while the heart
still remains empty and the sinus remains under the same conditions
as before ; in other words we can feed the ventricle without feeding the
sinus and without distending the heart. Among the numerous problems
to the solution of which we may hope that this method may give some
insight I will confine myself in this place to one, viz. the effect upon
the automaticity of the ventricle of a supply of blood through its
coronary system.

After the cannula had been inserted into the aorta a small portion
of defibrinated blood solution (1 sheep’s blood to 2 normal saline) or of
normal salt solution was sent through the coronary system in order
to remove the coagulable blood in the vessels ; the heart was suspended
and the junction wall cut across; the blood solution was then again
allowed to run through the coronary system at a constant pressure
varying from 50 to 70 mm. Hg. The blood solution dropped from the
cut ends of the coronary veins, the heart remained undistended as
before, and the ventricle responded to the contractions of the sinus
and auricles. The influence of the sinus was then removed either
by a section through the auricles intermediate between the sinus and
the ventricle or by the removal of the whole auricle. In no case have
I seen any sign of stand-still following upon the isolation of the
ventricle under these circumstances ; an immediate regular ventricular
rhythm was always observed.

Thus : —

March 7.

8.

14.

15.

„ 16.

Rate of the ventricular beat immediately after separation was
regular at 1 in 18 secs, and in 35 min. it had increased to
1 in 1 2 secs.

Rate immediately after separation 1 in 15 secs, and in 45 min.
still 1 in 1 5 secs.

Rate varied with blood pressure, quickest when the pressure
was highest, was perfectly regular at 1 in 6 secs., i.e. the
sinus rate.

Rate immediately after separation 1 in 8 secs, perfectly regular,
blood running through at the time, varied according to pres-
sure, quickest rate being 1 in 5 secs., i.e. same rate as sinus.

Rate immediately after separation 1 in 20 secs., no blood through
at the time, varied with blood pressure up to maximum rate
of 1 in 5 secs., i.e. rate of sinus.

PH. IV.

6

60

W. II. GA8KELL.

March 17. Rate immediately after separation 1 in 12 secs., no blood through
at the time, varied with blood pressure up to the maximum
rate of 1 in 6 secs., L e. about the same as the sinus rate.

Every experiment shows that the flow of blood through the coronary
system not only causes the independent rhythm of the ventricle to
be developed much more rapidly, but also that the rhythm of the
isolated ventricle when so developed may be as regular and as rapid
as that of the sinus, provided that the pressure of blood in the coronary
arteries is sufficiently great.

Again, not only is the whole ventricle capable of initiating and
sustaining a rate of rhythm as great as the normal sinus rate, but
also the suspended strip from the apex can be taught to beat as quickly
and as regularly as the sinus itself. Thus in the example already
mentioned (Fig. 3, PI. II., see p. 64) the whole heart had been pre-
viously suspended in order to show Prof. Horvath the action of the
vagus, and its rate was then found to be perfectly regular at ten beats
per minute. The apex strip in between 2 to hours after preparation
and suspension was heating spontaneously, as shown in Fig. 3, curves iv.,
V., at the rate varying from 9‘5 to 10 beats per min., and at 9'15 p.m.,
i.e. six hours after suspension and nearly five hours after the commence- .
ment of automatic contractions, at the rate of 10 heats per min. Since
then, the whole auricle is able of itself to heat as fast as the sinus,
while the rate of the automatic rhythm of the ventricle or of a strip of
ventricular muscle can be developed up to the same extent by the
trophic action of nutrient material or of the interrupted current respec-
tively, it is impossible on the ground of differences in the rate of
rhythm to make such a vital distinction between the origin of the
rh3fthms of the sinus and apex strip as is implied in the terms nervous
and myogonic applied to them respectively.

To sum up then : Between the rhythm of the sinus and the rhjfthm
of the muscular strip from the apex no hard and fast line can be drawn ;
between these two extremes a distinct gradation of rh3dhmical power
is manifested, and wherever such automatic rhythm is developed the
laws of its development are the same. What differences there are, are
differences of degree not of kind. In all cases the development of the
automatic rhythm to its fullest extent is a gi’adual one, commencing
with beats at a slower rate than that subsequently attained, and the
preliminary standstill which so often occui-s is simply a sign of this
gradual development.

INNERVATION OF THE HEART.

61

PART II.

On the sequence of the contractions of the different heart

cavities.

Just as Haller and the physiologists of his time looked upon the
rhythm of the heart as due to the action of the blood upon the muscular
tissue of the heart, so also they spoke of the t3q>e of the heart’s movements
as a peristaltic contraction which started in the venae cavae and spread
in regular order over the whole heart. In those days the continuity of
the cardiac muscular fibres was not fully appreciated and in consequence
arguments were given and experiments made to show that the contraction
of each muscle fibre caused a contraction of the next muscle fibre
because the act of contraction pinched compressed and stimulated nerve
fibres which supplied the muscle fibre next in order. The peristaltic
contraction then was looked upon as due rather to a progressive nervous
action than to the passage of a wave of contraction over a hollow muscle.
It was soon felt however that the type of a peristaltic contraction was
unsatisfactory, since the different parts of the heart were able, especially
when the heart was dying, to contract singly and separately. Schiff’
therefore came to the conclusion that the sequence is regulated from
the starting point of the rhythm, and that the ventricle contracts after
the auricle because, although the motor nerves of the auricle and ventricle
are stimulated at the- same moment in the venous _ sinus, the nervous
arrangements are of such a character that the stimulus does not reach
the ventricle so soon as the auricle. Of late years the conception of a
peristaltic wave of contraction passing from one end of the heart to the
other seems entirely to have dropped out of sight, and the sequence of
the contractions as well as their origin is attributed to the action of
motor nerve cells. Thus Eckhard’* and Marchand® both assert that
the sequence of ventricular upon auricular contraction is lost when the
two auriculo-ventricular ganglia are extirpated in the frog, and from the
experiments of March and — which show that the time between the ex-
citation of the auricle and the resulting contraction of the ventricle
is too long to be explained by a wave of contraction passing along
such a muscular tissue as that of the frog’s ventricle, — it has been
generally argued, that thp path of the excitation from the auricle to the

* Op. cit. 2 Jieitrdge, Vol. vii., p. 191.

3 Pfluger’s Archiv, Vol. xvn., p. 137.

6—2

62

W. R. GASKELL.

ventricle passes through the auriculo-ventricular ganglia. At the same
time, Eckhard' and others have observed that section of the inter-
auricular septum and therefore of the large nerve trunks between the
sinus and the ventricle does not in any way affect the sequence of
ventricular upon auricular beat. Here again, as in the investigation of
rhythm, the heart of the tortoise offers great advantages over that of
the frog from the fact that the intra-cardiac nerves and ganglia as
they pass from the sinus to the ventricle are situated externally and
not internally. In all cases the ganglia are rather to be considered as
appendages to the nerves than as separate organs to which nerve fibres
pass ; the largest accumulations of them are found at the bifurcation of
large nerve trunks in the sinus, in the junction wall between the two
auricles, and in the termination of this wall in the auriculo-ventricular
ring. In all these places the ganglion cells are also found on the smaller
branches of the nerves which ramify over the sinus and form a rich
plexus in the junction wall between the two auricles and at the
junction between auricles and ventricle. The nerves with their ac-
companying ganglia are distributed around the whole junction of the
sinus and the auricles, and from this ring as well as laterally from both
sides of the junction wall between the two auricles nerve fibres with
ganglia are plainly seen passing into the auricular tissue ; as the nerves
pass further into the tissue the ganglia become more and more scarce
and soon disappear. If then we call the junction wall between the two
auricles the flattened part and the rest of the auricles the bulged part of
the auricles, we And that the larger nerve tranks and ganglia of the
auricles are found only in those parts of the bulged portion which are
in the immediate vicinity of the flattened portion, of the sino-auricular
junction and of the auriculo-ventricular junction. Again at the junction
of the auricles and ventricle the nerve tranks passing from the junction
wall of the two auricles anastomose and form a rich plexus containing
large groups of ganglion cells along the line where this junction wall
passes into the auriculo-ventricular ring, along that is the side of the
ring furthest removed from the aorta, — this I will in future call the
“base” of the auriculo-ventricular ring. From thence a plexus of
nerve fibres, also containing ganglia though much more sparingly than
the basal portion, passes round the auriculo-ventricular ring. From
this ganglionic nervous ring, fibres ramify over both the ventricle and
the auricles, in each case accompanied by ganglion cells for a short

* Op. cit.

63

INNERVATION OF THE HEART.

distance. Similarly the junction between the sinus and the auricles
contains a ganglionic nerve plexus ring, and over the whole surface of
the sinus nerve fibres anastomose and carry ganglion cells with them.
In some cases the two vagi nerves join together in the sinus to form a
perfect chiasma as is also often the case in the frog, in others they run
slightly apart and join simply by anastomosing branches, as according to
Ranvier is the usual method in the frog. When they form a chiasma
the junction is filled up with a very large group of ganglion cells. The
nerve trunks passing from the sinus to the ventricle along the junction
wall are accompanied by the coronary veins in their passage from the
auriculo-ventricular groove to the sinus. One of these coronary veins
runs free from the surrounding tissue so as to form a separate and dis-
tinct connection between the sinus and the auriculo-ventricular groove
(C in the Figs. 20, 21); this vein can therefore be cut and either
end stimulated without any injury to the heart itself. A branch of the
right vagus nerve in the majority of cases accompanies this vein and is
usually large and well defined but sometimes small and insignificant.
This inter-cardiac nerve I propose to call the “coronary nerve”. It
branches off from the right vagus directly after the nerve has left the
large group of ganglia in the sinus and is well supplied with ganglia
until it is entirely free from the heart ; during its free course it contains
very few if any ganglion cells and just before it enters the auriculo-
ventricular groove ganglia again become abundant. In the auriculo-
ventricular groove it is in connection with a large group of ganglion
cells, anastomoses freely with the ganglionated nerve plexus of the
groove, and is distributed over the auricles as well as the ventricle. Its
auricular fibres as well as its ventricular are supplied with ganglia for a
short distance. The cardiac nerves then after they leave the sinus form
two ganglionated nerve rings at the junctions of the sinus and auricles
and of auricles and ventricle respectively, connected by a ganglionated
nerve plexus band in the junction wall between the two auricles.
In Fig. 21, p. 49, the appearance of the heart when suspended is
represented; the curved line C represents the free coronaiy vein and
nerve, and the line directly joining the sinus S with the ventricle V the
position of the junction wall between the two auricles. A vertical cut
therefore between S and V will divide this junction wall and with it
all the nerves which pass directly from the sinus to the ventricle.

In endeavouring therefore to find out the reason of the sequence of
the heart contractions, we can at the outset eliminate the hypothesis
that stimuli pass from the sinus to the auricles and ventricle through

64

W. II. GA8KELL.

the cardiac nerves and attached ganglia, and that the function of the
latter is to regulate the time of arrival of the stimulus at the ventricle,
so that the ventricle may always contract in due sequence to the auricle.
For, section of all the nerve trunks between the sinus and ventricle or
even absolute removal of them with their accompanying ganglia does
not in the very slightest degree alfect the due sequence of ventricular
upon auricular beat. Again, on the other hand, if the auricles be cut
away from the ventricle leaving only the coronary nerve as the link of
communication between the sinus and the auriculo-ventricular groove,
there is never the slightest sign on the part of the ventricle and the
auricle in connection with it of any ability to beat in response to the
rhythm of the sinus and that part of the auricle in connection with it.
Since then the sequence of ventricular upon auricular beat does not
depend upon the transmission of stimuli along nerve fibres fi'om the
starting point of the rhythm to the auricle and ventricle respectively,
what does it depend upon ? The answer to this question is simple and
perfectly certain, viz.

The ventricle contracts in due sequence with the auricle
because a wave of contraction passes along the auricular
muscle and induces a ventricular contraction when it reaches
the auriculo-ventricular groove.

We have seen that a slit can be made through the junction wall and
that part of the auricle in connection with it without at all interfering
with the sequence of the beats. We can further carry this sHt much
nearer to the point of attachment of the ligature at the apex of the
auricle so that, the other auricle being cut away, the connection
between the sinus and the ventricle is maintained by two bands of
auricular tissue joined at their apex by a narrow bridge of tissue as
shown in the accompanying woodcut Fig. 22 ; and yet the due sequence
of the ventricular upon the auricular beats is not disturbed. That part
of the slit-up auricle which is in connection with the sinus will be called
in 'future “ sinus-aui'icle ” or A^, and the part m connection with the
ventricle, ventricle-auricle or A^.

When the auricle is slit up for only a short distance so that the
bridge of tissue at the apex is broad, then the auricle contracts as a
whole and the ventricle follows just as though no section had been made.
The section can be continued further and further without much differ-
ence in the result ; at last however, when the bridge is quite thin, it is
apparent that a wave of contraction passes from the sinus up A^ and
then after a slight pause down A^. to the sulcus where another pause

65

INNERVATION OF THE HEART.

occurs and then the ventricle contracts. In Fig. 4 A, PI. III. the graphic
representation of these pauses is shown together with the due sequence

Fig. 22. Junction wall and auricle slit up so as to separate auricle into 2 parts As, Av.

of the ventricular upon every auricular beat. When the section is still
nearer the apex then it is seen that every contraction wave is unable to
pass the narrow bridge of tissue, but that every second contraction passes
over and when it reaches the ventricle induces a ventricular contraction.
The ventricle mver contracts in response to those alternate contractions
of Ag which do not pass the narrow bridge of tissue at the apex, but only
when the contraction wave passes down A^ and reaches the auriculo-
ventricular sulcus. By the right amount of auricular section then we can
make the ventricle beat perfectly regularly after every second beat of the
sinus. The nature of the curves obtained is seen in Figs. 4, 10, 11, 12, 13,
PI. III., IV. Fig. 4 B is taken from the same experiment as Fig. 4 A, in
order to show graphically the effect of slightly increasing the severity
of the section. As the section is continued nearer the attachment of the
ligature so that the bridge of tissue is still further reduced the contrac-
tions pass with greater and greater difficulty, so that a contraction wave
passes along Ay after perhaps .5, 6 or more heats of Ag and then and then
only the ventricular contraction follows. Finally when the tissue is so
thin that it often appears impossible to cut further without cutting the
ligature itself, then the contraction wave is absolutely unable to pass, then

66

W. II. GASKELL.

the “block*” is comiDlete and any contractions of the ventricle which
may occur are absolutely independent of those of the sinus and sinus-
auricle. Even when the block is complete so that no contractions have
been able to pass for many minutes and the independent ventricular
contractions have commenced, it is still possible as will be shown later
on for a more or less complete recovery to take place, so that again
every or every second contraction may pass the blocking point.

These experiments show definitely that the ventricle contracts
after the auricle only when a contraction wave passes to the
auriculo-ventricular groove, and I have never seen any evidence
that anything of the nature of a nervous infiuence such as a wave of
excitation can pass the block and set the ventricle in action when the
contraction wave cannot pass. It is certain that no nervous influence
passing along nerve fibres in the visceral pericardium apart from the
muscle fibres is concerned in the production of the ventricular beat, for,
after having slit up the auricle slightly so as not to cause any block, I
have then thinned down a small ring of tissue in midway between
the attachment of the ligature and the ventricle in such a manner as to
remove all the pericardial surface, and therefore to leave at this spot
a connecting bridge of muscular tissue alone ; through this the contrac-
tion wave passed and a ventricular contraction followed. By thinning it
sufficiently a partial block, so that every second contraction passed, or a
complete block could be caused. When the contraction wave reached the
ventricle it responded, when no contraction passed the ventricle remained
quiescent ; in fact, no doubt can possibly remain that the ventricle beats
after the auricle because it does not contract until the auricular contrac-
tion reaches it.

In precisely the same way the due sequence of the contractions in
the fi’og’s heart does not depend upon the integrity of the nen’^es in the
auricular septum but upon the contraction of the auricle, and here also
as I have elsewhere'^ sho^vn a blocking of the auricular contraction wave
can be caused by compression of the muscular fibres as they pass into
the auriculo-ventricular groove, a block which may be partial or complete
in precisely the same way as already described for the tortoise.

1 In his experiments upon the passage of contraction waves along the muscular tissue
of the swimming bell of theMedusm, Romanes (Phil. Trans. Vol. CLX^^. Ft. i.) has through-
out made use of the term “ block ” to express any artificial hindrance to the passage of the
contraction. I therefore make use of the same term in speaking of the results of experi-
ments on the cardiac muscle which are very similar to those which ho performed on the
muscle of the Medusa.

2 Phil. Trans. 1882, Ft. iii.

INNERVATION OF THE HEART.

67

Since then the ventricle does not contract after the auricle because
separate stimuli pass from the sinus to the ventricle along nerve fibres,
but does contract because a contraction wave passes along the muscular
tissue of the auricle to the junction of the auricles and ventricle, the
question arises; How is it that a contraction of an auricular muscle
fibre is able to cause a contraction of a ventricular muscle fibre ? and
especially, what is the reason of the pause which ensues before the
ventricle contracts after the auricular contraction has reached the
auriculo-ventricular groove ?

An answer to these questions is most likely to be found by examining
whether any particular portion of the junction of the auricles and
ventricle is especially concerned with the maintenance of the sequence
of ventricular upon auricular beats, and at the same time investigating
the structure of the auriculo-ventricular groove. For the purposes of
description it is convenient to divide the auriculo-ventricular ring into
sectiorrs, and therefore in accordance with its position in all my experi-
ments I ■will call the portion of the ring or rather of the half ring
near’est the aorta, the upper, or A in the accompanying diagram, the
lateral portion the middle or B, and the lowermost portion the basal
segment or C.

In the first place the integrity of the whole ring is unnecessary for
the due sequence of the contractions ; the whole of one auricle can be
removed together with the corresponding half of the base of the ventricle,
and yet the contractions of the remaining auricle will be followed
regularly by contractions of the ventricle. I commence therefore by
cutting away the left auricle and that part of the ring to which it is
attached, and then remove the auricular attachments and the ring
on the right side bit by bit until the sequence is lost, beginning in the
one case with the removal of the basal portion C and cutting round
towards the aorta and in the other with the removal of the upper section

68

W. II. GASKELL.

A and gi'adually passing towards the base. The following example
shows the difference in effect of the two operations.

July 5, 1882. Upper portion of tortoise removed from the body with the
heart in position, and placed on a plate. The left auricle and the base of the
ventricle to which it was attached was cut away. The ventricle still con-
tracted after every contraction of the right auricle.

The base 0 of the right part of the auriculo-ventricular ring was then
removed, together with that part of the right auricle which was attached to
it. The ventricle still beat absolutely synchronously with the auricle.

The middle B of the right side of the ring and the auricular attachments
were cut away. Still every contraction of the auricle induced a ventricular
contraction.

The section was then carried close to the aorta, so that the only part of
the auriculo-ventricular ring which was left intact was that part of the upper
portion A of the ring on the right side between the middle Une and the whole
attachment of the aorta.

After this last section at 1.9 p.m. the ventricle remained quiescent for a
while, then contractions began to pass from auricle to ventricle and in ten
minutes, at 1.19 p.m., the ventricle was contracting regularly after every second
auricular contraction.

1.30 Ventricle stiU misses every second auricular beat.

1.40 do. do.

1.52 Ventricle misses only every third beat.

1.59 Ventricle misses only, every fourth beat.

At 2 p.m. I cut away a small piece of the ring at the middle line of the
upper part of the ring where the right and left auricles meet.

2.5 Ventricle beats after every contraction of the auricle.

2.9 do. do.

2.12 do. do.

At 2.13 I cut from the middle line towards the aorta up to the middle
of the attachment of the aorta, so that the auricle was now attached to only
a narrow strip of the auriculo-ventricular rmg comprising the middle of
the attachment of the aortic trunk. AJter this last section the ventricle
was quiescent but again

at 2.17 was beating after every second auricular beat,
and at 2.19 was again synchronous with the aui’icle.

A small piece of tissue was again removed underneath the aorta. V entricle
immediately quiescent.

At 2.25 the sequence had again recovered to the extent that the ventricle
was able to respond to every second auricular beat.

The strip of auricular tissue was then cut away, and the ventricle was

INNERVATION OF THE HEART. 69

found to be beating spontaneously at a rate somewhat slower than 1 to 3
auricular beats.

The last small piece of the auriculo-ventricular ring was now cut away
at 2.28. The ventricle immediately became quiescent and remained without
a single contraction as long as observed, i.e. up to 3.30 p.m.

A second tortoise was now taken and the reverse operg,tion performed, the
left am’icle and auriculo-ventricular ring being cut away at 2.44 p.m. The
ventricle responded regularly after every contraction of the right auricle.

The upper portion of the right ring and the attachments of the right
am’icle were now cut away from the upper middle line to the end of the
attachment of the aorta at 2.49. The ventricle immediately remained
quiescent.

2.57 Still quiescent.

3.4 do.

3.45 First ventricular beat.

3.12 Ventricle beats alternately after every second and every tliird
auricular beat.

3.15 StiU alternately after every third and every second beat.

3.22 Ventricle beats regularly after every second auricular contraction.

3.25 do. do.

The middle portion B of ring was now removed, leaving the whole of the
broad base 0 with its nerves, ganglia and auricular attachments still intact.

The ventricle was immediately quiescent ; observed up to 4 p.m. ; the
ventricle never responded with a single contraction although the auricles
continued to beat regularly and well.

This experiment shows clearly that the basal part of the auriculo-
ventricular groove has the least share in the maintenance of the sequence
of ventricular and auricular beat, and yet this is precisely the part
where the nerve fibres enter, where the ganglion cells are to be found in
greatest profusion. From this fact alone the assumption that ganglion
cells play an important part in the transmission of the contraction from
the auricle to the ventricle is rendered very doubtful ; and microscopical
evidence shows that such an assumption is not only improbable but
unnecessary.

The heart of the tortoise consists of three muscular cavities, the sinus
cavity, the auricular cavity and the ventricular cavity, separated from
each other by two more or less well defined constrictions, the auriculo-
ventricular and sino-auricular grooves. The arrangement of the muscular
fibres is somewhat as follows. In the sinus the muscular fibres are
closely set together, largely parallel to each other, with a tendency to

70

W. H. GASKELL.

form a cii’cularly arranged continuous muscular sheet, and from these arise
and branch in various directions other fibres which form separate bundles,
passmg from point to point and constituting a rudimentary reticulated
structure similar to what is seen in perfection in the auricles. At the
sino-auricular junction both sets of fibres join to form a regular band
of 23arallel closely-set muscle fibres which form a circular
muscular ring, from which the fibres of the auricle take their
origin. On both sides of this ring, whether in the sinus or the auricle,
those fibre bundles which pass towards it at right angles to the direction
of its fibres split into two parts, which curving in opposite directions
are continuous with the ring fibres. From this sino-auricular muscular
ring a network of loose reticulated fibres connected in all directions
springs to form the bulged portions of the auricles. In the flattened
portion of the two auricles — in, that is, the band of tissue forming the
junction wall between the auricles, the muscle fibres are arranged in
a closely-set sheet of fibres which are continuous with and largely
parallel to the circularly-arranged fibres of the sino-auricular ring.
This portion of the auricles then resembles in the arrangement of its
muscular structure the ground-work of the sinus and the sino-auricular
ring, and not the reticulated mesh-work of the rest of the auricles.
From the sino-auricular ring and firom the junction waU, the reticulated
fibres of the auricle ramify in all directions until they approach to
their attachments in the upper and middle parts of the auriculo-
ventricular groove. Here again as in the sinus the arrangement gradually
changes from a network into a continuous sheet, the fibres become
more and more parallel, and at last form another well defined
circularly arranged ring of parallel muscular fibres. From
this ring the muscular fibres of the ventricle in part take their origin.
The base of this ring is continuous with and its fibres are parallel to
the non-reticulated muscular fibres of the inter-auricular junction wall.
We see then that the arrangement of the muscle fibres in the heart of
the tortoise, the two rings of circularly arranged muscle fibres joined at
their base by a band of similarly circularly arranged fibres is very
suggestive of the primitive origin of the heart from a tube like that of
an artery or of the ureter, where the fibres are throughout aiTanged in
a circular manner. The existence of these two muscular rings connect-
ing the three muscular cavities of the heart is amply sufficient to
account for the passage of the contraction from the sinus to the aui’icle,
and from the amide to the ventricle, without the necessity of invoking
the presence of ganglion ceils, and leads directly to the view originally

INNERVATION OF THE HEART.

71

held by physiologists that the cavities of the heart contract in regular
sequence, because a peristaltic wave of contraction commencing at the
sinus passes from one end of the heart to the other.

Before this view can be accepted some explanation must be given of
the natural pauses which occur between the contractions of the sinus
and auricles and of the auricles and ventricle respectively. Also atten-
tion must be paid to Marchand’s* assertion that the time which elapses
before the ventricle responds when a stimulus is applied to the auricle is
too long to be explained on the assumption that the stimulus reaches
the ventricle along simple nerve or muscle fibres, as well as to the
assertion that the ventricle of the frog does not contract after the auricle,
when the two auriculo-ventricular ganglia have been removed.

We have already seen that an additional pause as well marked as
either of the natimal pauses can be artificially produced in a purely
muscular part of the auricles by a simple hindrance of the passage of a
wave of contraction. Such a commencing block is caused when the path
of the contraction wave is narrowed to a thin bridge of muscle, the
conduction power of which has moreover been in all probability lowered
by the previous operation. It is therefore possible to intei’polate a
pause in the course of a wave of contraction by artificially altering the
conduction power of the muscle at any one point. If then such an
alteration of conduction power occurred naturally at any point owing to
the normal arrangement or structure of the muscle fibres at that point,
a pause or rather an alteration of rate in the progress of the contraction
wave would take place here of the same character as the pause between
the contractions of the auricle and ventricle.

Further, such an alteration in conduction power in the course of the
passage of the contraction wave from the auricle to the ventricle would
explain all the objections which have hitherto been raised against the
hypothesis that the beat of the heart is a peristaltic wave of contraction
passing from one end of the heart to the other. Thus in the first place
such an assumption will explain Marchand’s experiment mentioned
above ; for the whole point of that experiment is based on the supposi-
tion that the rate of conduction along a supposed muscular path from
the auricle to the ventricle must be equal to the rate along the muscles
of the body of the ventricle as determined by the experiments of Engel-
mann. In the second place the facts — that under certain conditions,
especially when the heart is near to death, a contraction of the ventricle

* Loc, cit.

72

W. II. GASKELL.

alone can be caused which does not induce an auricular contraction and
vice versd ; and also that in the same circumstances of lowered excita-
bility whether caused by impaired nutrition or by the action of poisons,
&c. the ventricle is often found to be beating after every second, every
third or more auricular beats, and finally to cease beating while the
auricle continues to contract — which were in the eyes of Schiff, Volk-
mann, Budge, &c. insuperable objections to the acceptance of a peristaltic
wave passing from auricle to ventricle, have now I venture to say
become the strongest arguments for the existence of such a peristaltic
wave, which at the auriculo- ventricular junction passes through a region
of diminished conductivity. Just as in the passage of the contraction
from the sinus-auricle to the ventricle-auricle a successively increasing
severity of section, that is, an increasing impairment of the tissue, pro-
duces first a commencing block, i.e. a simple delay in the rate of the
passage of each contraction wave, then a partial block, so that only every
second contraction passes, and finally a complete block, in which no con-
tractions pass; so too any impairment of the whole heart of such a
character as to lower the excitability and the conduction power of the
cardiac muscle will necessarily convert the sHght block which exists
naturally at the auriculo-ventricular junction into first a partial block
during which the ventricle will respond to every second, third, or more
beats of the auricle, and finally into a complete block when the auricles
will continue beating but the ventricle wiU remain quiescent. The
special tendency for the contraction wave to be blocked at both the
sino-auricular and auriculo-ventricular junctions will be further con-
sidered when we come to deal with the action of the cardiac nerves.

Further, we have every reason to believe that the contraction wave
is not likely to pass so easily from the auricle to the ventricle as over the
surface of the auricle or ventricle themselves, not only because the
auriculo-ventricular muscular ring is narrow and a somewhat abrupt
change occurs in the direction of the muscular fibres along which the
contraction wave passes, when it reaches and leaves this ring, but essen-
tially because the structure of the muscular fibres here is different from
those of the auricle or ventricle. This difference of structure can be
best discussed in connection with a description of the structure of the
muscle fibres in all the different joarts of the heart of the tortoise.

The muscle fibres throughout the heart are of the same 13^)0, any
differences which are seen are differences in the prominence of the
various structural peculiarities of the cardiac t}’pe of muscle, and are
not so great as the differences between unstriated and striated muscle

INNERVATION OF THE HEART.

73

fibres. Thus all the muscle fibres are to a greater or less extent trans-
versely striated ; but the prominence of this striation varies considerably.
Similarly the thickness of the fibre, the extent of parallelism of its
edges, the size of the nucleus in relation to the size of the fibre, and
therefore the extent of crowding of the nuclei in any strip, all present
differences in different parts of the heart. The greatest contrast is seen
when the muscular fibres of the ground layer in the sinus are teazed out
and compared with the muscle fibres of the spongy tissue of the ventricle.
The sinus muscle fibre is thin and delicate, tapering somewhat at both
ends, with a large central oval nucleus which causes a distinct bulging
of the fibre ; the substance of the fibre shows a striation which is
decidedly indistinct, presenting often a granular rather than a distinct
banded appearance. On the other hand the ventricular muscle fibre is
boldly and strongly striated, it is much thicker than that of the sinus,
its edges are parallel and the thin elongated nucleus is small in com-
parison to the size of the fibre. The muscle fibres of the reticulated
tissue of the auricle are not so large or so coarsely striated as those of
the ventricle, though larger and much more distinctly striated than the
sinus muscle fibres. Their edges also are more parallel than in the
fibres of the sinus. The muscular ring forming the junction of the
auricles and ventricle, and to a certain extent the whole junction
wall joining the two amdcles are composed of muscle fibres with a
structure intermediate between the sinus and the auricle muscles.
The nuclei are large, conspicuous on section both in size and number,
the striation is not so well marked as in the bulged portion of the
auricles, and the fibres are thin and delicate with somewhat parallel
edges.

Such a structure as above described is very suggestive not only as an
explanation of the pauses which occur naturally in the course of the
peristaltic wave of contraction, but also of the differences of rhythmical
power exhibited by different parts of the heart. We see that the sinus,
the sino-auricular ring, the junction wall between the two auricles and
the auriculo-ventricular ring are all composed of muscular fibres which
differ from those of the ventricle and the bulged portions of the auricles
not only in arrangement but also in structure, and that this difference is
exactly what we should expect to see, if these latter parts had reached a
higher stage of development than the former. The more developed
tissue would not only possess a more marked striation, a less conspicuous
nucleus and a contour with parallel edges rather than spindle-shaped,
but would be characterised by a greater rapidity both of contraction and

74

W. II. GASKELL.

conduction than the less developed. If then a wave of contraction were
started at the sinus end it would pass most rapidly along the reticulated
fibres of the sinus, auricles, and ventricle, and more slowly at the junc-
tions of the sinus with the auricle, and of the auricle with the ventricle ;
if further these more rapidly contracting parts were bulged out so as to
conceal the junctions, then the true nature of a wave of contraction
would be completely masked, and the contractions of the three cavities
of the sinus, auricles and ventricle would appear to take place indepen-
dently with pauses between them.

The difference in the conduction power of the muscular tissue of the
inter-auricular junction wall firom that of the auricle proper, is evident
from a number of experiments which I have made for the purpose of
comparing the efiect upon the sequence of the ventricular and auri-
cular contraction of removal of the junction wall alone, leaving the
bulged portion of the auricles as the means of communication between
the sinus and the ventricle, and conversely of removal of the bulged
portions, leaving only the junction wall between the two auricles.
The following example is typical of the opposite effects of these two
operations.

March 10, 1882. Two small tortoises were taken and their hearts
removed and pinned out with the junction wall uppermost. In each case
the free coronary vein and the flattened portion of the auricles was well
defined. The line of junction of the bulged and flattened portions was cut
through on each side in both cases, without affecting the sequence, and then
in the one case the whole of the junction wall was cut away leaving the
bulged portion intact, and in the other the bulged portions were separated
from the ventricle leaving the junction wall intact. In the first case the
sequence was absolutely unafiected by the operation, in the other the ventricle
remained still for a long time and then began to beat slowly and inde-
pendently of the auricular cbntractions. In the first case the auricular
tissue was then cut through to a greater and greater extent, imtil at last only
a narrow bridge of the reticulated muscle of the auricle remained, and yet
the sequence was maintained. In fact, the sequence of ventricular upon
auricular beat is able to continue when the contraction wave is obliged to
pass over an exceedingly narrow bridge of the muscular tissue of the bulged
portion of the auricle, but is absolutely lost, when the only path for the
contraction wave is the flattened junction wall between the two auricles,
although in the latter case the strip of muscle is much broader than in the
former and although in both cases the auriculo-ventricular ring is intact.

The difference between these two cases is most striking and is

INNERVATION OF THE HEART.

75

always the same, although the band of tissue which was left intact in
the first case along which the contractions might travel to reach the
ventricle, was many times broader than the final bridge of the reticulated
muscular tissue in the second case ; although, in addition to the greater
breadth of the strip, the nerve communications ganglia and all, between
the sinus and the ventricle were intact in the first experiment while in
the second nothing was left but a nari’ow muscular bridge as the means
of communication between sinus and ventricle; yet the sequence was
absolutely prevented in the former case, absolutely unaffected in the
latter. We see then without doubt not only that the sequence depends
on the passage of a contraction over the bulged portion of the auricles to
the upper portion of the auriculo- ventricular junction ring, but also the
conduction of the contraction is less easy along the muscular tissue of
the junction wall between the two auricles than along the reticulated
muscular network of the bulged portion of the auricles. I do not
desire to assert that a contraction wave can never pass along the inter-
auricular junction wall and so to the ventricle, for I have seen in one or
two cases a slight and partial repair of the sequence some time after the
operation when the junction wall alone was left; I only assert that in all
cases the sequence is maintained with immensely greater ease when
only a small bridge of the reticulated muscular tissue is left, over which
the contraction wave can travel, than when the whole of the junction
wall is left intact.

Finally, the assertion based upon the experiments of Eckhard and
Marchand, that the auriculo-ventricular ganglia are essential for the
due sequence of the ventricular upon the auricular contractions in the
frog, must be examined into and its truth or falsity proved.

The fibres of the auricles in the frog pass into a well defined ring of
circularly arranged muscle fibres at the junction between the auricles
and ventricle of the same nature as already described for the tortoise.
The diameter of this ring is naturally as small as the orifice between the
auricles and the ventricle, so that in such an operation as the removal of
the auriculo-ventricular ganglia it is easy to cut away or damage this
muscular ring, even while apparently leaving the connections between
auricles and ventricle intact. I have however succeeded in removiur.-
the two ganglia without injury to this ring as follows. I first opened
and removed a portion of the apex of one auricle, washed out and at the
same time slightly distended the heart with a jet of normal saline solu-
tion, so as to bring the septum into view : I then seized the septum
with a pair of fine forcejis and gently drew it forward, until the two white
PIT. IV. 7

76

W. II. QASKELL.

masses of the auriculo-ventricular ganglia could be plainly seen. With
a fine pair of scissors the septum and the two white masses were now
carefully cut away, great care being taken not to injure the auriculo-
ventricular ring itself. After the operation the sequence con-
tinued just as well as before, every auricular contraction was
followed by a ventricular contraction without any prelimi-
nary standstill or alteration of any kind. The parts that had
been cut away were placed in osmic acid, and the two nerves of the
septum terminating in the two well-kno^vn bulbous ganglionic masses
together with portions of the auriculo-ventricular valves were well
shown.

From what has been already said, it is evident that if this muscular
ring be either- much injured or cut away, a more or less complete block
in the passage of the contraction from auricle to ventricle must take
place, just as a block can be always caused in the passage of the con-
traction wave from any one to any other part of the heart of the tor-
toise. Eckhard’s^ description of the result of his experiments shows
to my mind clearly that he had produced, by his method of procedure,
such a block, which at first was complete, so that the ventricle remained
still, then Was partial, so that a certain number of contractions of the
ventricle took place, and finally had almost though not quite disap-
peared. The dependence of these ventricular contractions, which he
observed after extirpation of the two ganglia, upon the contractions of
the auricle, and therefore the independence of the sequence upon the
integi’ity of these ganglia, could not require a better proof than he him-
self gives^ viz. that stimulation of the vagus outside the heart
brings these ventricular contractions to rest at the same
time as the contractions of the auricle. In other words, stimula-
tion of the nerve is able to influence in the same manner, at the same
moment and to the same degree, the contractions of the auricle and these
supposed independent contractions of the ventricle, although the nerves
of the septum and the two auriculo-ventricular ganglia had been removed.
If, then, the ventricular contractions in this case wei’e really independent
of the auricular, the influence of the vagus must have passed to the
ventricle over the tissue of the auricles, apart from the direct route by
the large nerve trunks from the sinus to the ventricle ; a mode of
action which is not only extremely unlikely, but is also contrary to all
experimental evidence afforded by the heart of the tortoise. If, on the

^ Op. cit.

Op. cit., p. lo.*?.

INNERVATION OF THE HEART.

77

other hand, these contractions were not really independent of those of
the auricle, but only appeared to be so owing to a blocking of the con-
traction wave in its passage from the auricle to the ventricle, then
naturally when all auricular contractions were stopped by the stimula-
tion of the nerve the ventricular contractions ceased also. Similarly the
experiments of March and* do not in the smallest degree prove that the
sequence of the contractions depends on the integrity of the auriculo-
ventiicular ganglia ; they simply show that if a sufficient amount of the
muscular ring at the auriculo- ventricular junction be cut away, the block
so caused may be permanent, and that in some of the pieces so cut
away ganglion cells may be found.

Again, from what has already been said in Part I., those very parts
which possess a less developed jnuscular structure possess also greater
rhythmical power than those which have attained a higher develop-
ment. As we pass from the sinus along the junction wall of the auricles
to the auriculo-ventricular ring, and from thence to the muscular tissue
of the bulged portion of the auricles and ventricle, we find evidences of
successive grades of rhythmical power in fair correspondence with the
grades of development of the tissue. The study of the development of
the heart shows that it is originally a simple tube with muscular walls
from end to end of which waves of contraction pass ; a portion of this
tube expands to form the auricles and another portion to form the ven-
tricle; these two being connected by an unexpanded part called the
canalis auricularis, which gradually disappears as the auricles and ven-
tricle bulge more and more, until the original tubular heart becomes
converted into a series of cavities with constrictions between them. If
m this process those parts which expand take on a higher development
for the purpose of executing more rapid contractions, and if this expan-
sion did not include quite the whole circumference of the auricular por-
tion of the tube, we should have in the adult heart the remnant of the
original tube represented both in the arrangement of its fibres and in
function by the ground fibres of the sinus, the sino-auricular ring, the
junction wall between the auricles, and the auriculo-ventricular rino'.
According to this view, then, we can conceive that the variations in
rhythmical power and in conductivity which are characteristic of the
different parts of the adult heart of the tortoise may all be accounted
for on the supposition, that the development of the muscular tissue of
the originally tubular heart has not proceeded at the same rate throimh-

^ Op. cil.

7—2

78

W. II. GA8KELL.

out tlie tube ; so that in the adult heart greater variations in rhythmical
power are apparent in the different sections of it than in the original
tubular heart ; the peristaltic wave of contraction which originally
passed smoothly from end to end, passes finally along a tube of irregular
calibre, the muscular walls of which have become so modified in their
rates of contraction and conduction, as well as in the arrangement of
their fibres, as to form out of a simple peristaltically contracting tube
such an efficient muscular pump as is represented by the adult heart.

Such a conception is entirely in accordance with all experiments
which I have had an opportunity of making on the hearts of animals
lower than the tortoise. In the skate especially, which possesses a large
strong muscular conus arteriosus, the passage of the peristaltic wave of
contraction can be easily observed. I have not yet had an opportunity
of studying the action of the skate’s heart to any extent ; the following
observations being the results of an examination of two large skates,
weighing respectively about 60 and 40 pounds, which I had the oppor-
tunity of making this last summer during a yachting trip along the
west coast of Scotland. The hearts were examined on the deck of the
yacht almost immediately after the skates were taken out of the water,
and were found to be beating vigorously and regularly, with a good
supply of blood in them. The muscular fibres of the large fleshy conus
arteriosus are arranged circularly, and merge imperceptibly into the
muscular structure of the ventricle. The heart beats somewhat slowly,
with great regularity, in the order auricle, ventricle, conus, and it is
plainly evident that the contraction passes along the conus in the form
of a peristaltic wave. Again, if the auricle is slit up in the same way as
described for the tortoise, a very long strip of auricular tissue is ob-
tained, along which each beat travels most plainly to the ventricle in
the form of a peristaltic wave, which again reappears as soon as the
contraction reaches the conus arteriosus. The peristaltic nature of the
beat of the whole heart could not be demonstrated more clearly than in
the simple heart of the skate. Further, the rhythmical powers of the
conus are nearly as great as those of the sinus ; when isolated it con-
tinues to beat with great regularity, waves of contraction following
one another as readily as in the case of the isolated sinus ; this rhythm
does not depend on any particular part, one piece continues to beat as
well as another.

What, however, is most striking of all, and shows the near relation-
ship between the rhythm of the conus arteriosus and of the sinus, and is
the strongest argument in favour of the development of the heart from an

INNERVATION OF THE HEART.

79

original muscular tube, of which the rhythmical properties are nearly
the same throughout, is the ease with which in the skate’s heart a reversal
in the order of the contractions can be brought about, i. e. the rhythmical
preponderance of the sinus end of the tube be transferred to the conus
end, and vice versd. If, when the heart is beating normally, the conus
arteriosus be touched with the sharp point of a knife, a contraction
wave is immediately started in it which when it reaches the ventricle
causes a contraction of the ventricle, and then in due sequence of the
auricle. After this interpolated contraction wave, due directly to the
stimulus, a slight pause takes place, and then for some minutes the
heart beats with regular contractions in the order conus, ventricle,
auricle, each beat commencing with a distinct peristaltic wave running
along the conus into the ventricle. Another slight pause then occurs,
and the heart resumes the normal order of its contractions. In both
the instances observed by me, the rate of the contractions started from
the conus end was somewhat quicker than the normal rate from the
sinus end. Further, if the sinus or junction of the sinus with the auri-
cles be gently stimulated, when in consequence of a previous stimulation
of the conus the order of the peristaltic contraction has been reversed,
then immediately a second reversal takes place, and the contractions
recommence at the sinus end. In this way I was able, by alternate
slight momentary stimulations of the conus arteriosus and of the sinus,
to make the heart of the skate beat in a way similar to the Ascidian
heart, in which the normal beat consists of a series of waves of contrac-
tion passing alternately in opposite directions. In fact, we see that in
the Ascidian the rhythmical power of the two ends of the heart is so
nearly equal, that the contractions start with equal, or nearly equal
facility from either end, and the alternation of the direction of the con-
tractions is in all probability due to some slight stimulus alternately
affecting first one and then the other end, such as an increased blood
pressure due to the flow of blood in one direction, which would act as
a stimulus chiefly upon that end towards which the contraction waves
had been previously travelling*. In the skate we reach a higher stage
than this, the difference between the aortic and venous pressures alone
does not constitute a stimulus sufficient to overcome the greater rhyth-
mical power of the sinus, and therefore to reverse the order of the con-

In the paper by Foster and Dew-Smith upon the effects of electricity applied to the
hearts of MoUusks (Proc, Roy. Soc. No. 160, 1875) an observation of Dew- Smith is men-
tioned, which showed that the interrupted current when applied to the heart of the Salpa
caused that he.art to beat for two minutes entirely in one direction.

so

W. II. GASKELL.

tractions; a slight mechanical stimulus is required in addition in order
to give such a preponderance to the rhythmical power of the conus arte-
riosus as is necessary for the i>roduction of a rhythmically contracting
heart, in which the direction of the contractions is reversed at regular
intervals. Again, the cardiac nerves of the skate, like those of all ver-
tebrata, enter the heart at the venous end, and from thence are distri-
buted over the heart; ganglia therefore are found plentifully in the
sinus, and disappear before the conus arteriosus is reached; in the
conus, as in the bulbus' of the frog, ganglia are not to be found. Not
only then does the skate’s heart afford a good example of the peristaltic
nature of the heart’s beat, but it also gives a new proof that the
starting point of these peristaltic contractions is determined
by the nature of the muscular substance rather than by the
presence or absence of ganglion cells.

In the frog, as well as in the skate, there is evidence to show that
the rh}dhmical powers of the muscular tissue of the bulbus are more
nearly allied to those of the sinus than of the bulged portions of the
ventricle. Thus Engelmann has shown not only that the bulbus is free
from ganglion cells, but also that its rhythmical power is much greater
than that of the muscular tissue of the ventricle. The length of the
standstill after isolation, the rapidity of development of its full rate of
I’hythm when distended with serum, and the regularity of that rhjdhm,
all point to a rhythmical power inherent in the muscular tissue of the
bulbus, which is greater than that of the muscular tissue of the apex of
the ventricle.

The conception advanced above, that the rhythmical beating of the
heard is due to a series of peristaltic contractions which start from that
particular portion of the muscular tissue of the heart in which the pro-
perty of automatic rhythm has been most largely developed, brings the
heard ’s action into harmony with the rest of the vascular system and
with the rhythmical properties which are so ofterr manifested by the less
specialized forms of muscular tissue. The experiments of Lrrchsinger*
have shown not only that the regular well-marked rhythrrr of the veins of
the bat’s wing is due undoubtedly to peripheral and not to cerrtral causes,
but also that the rhythm resembles that of the apex of the frog’s heart
in its dependence upon a certain amount of pressure withiir the veins
themselves. In tlris case then, as well as iir the strictly arralogous case

' See Engelmann, Op. cit.

^ Pfliiger’s Archiv, Vol. xxvi. p. 415.

INNERVATION OF THE HEART.

8i

of the middle third of the ureter', we have in all probability an instance
of a rhythm dependent upon the special development of a particular
function of the muscular tissue, and not upon the hypothetical existence
of ganglion cells.

PAKT III.

On the action of the cardiac nerves.

Stimulation of the vagus nerve in the frog is able to produce two
ojiposite effects upon the rate of rhythm of the heart, either slowing
and standstill or else acceleration. In my former paper, read before the
Royal Society in Dec. 1881 ^ I have shown clearly that these two effects
are so far independent of each other that the acceleration may occur
without any previous slowing. Again, the experiments of Nuel® have
shoum that the vagus can produce a diminution of the force of the
auricular contractions independently of any action upon the rate of
rhythm. In my paper I have shown that this diminution of the force
of the contractions occurs both in the auricle and ventricle and is
followed by a most remarkable increase in the force of the contractions,
and that these two effects are so far independent of each other that
the augmentation of force may occur without any previous diminution.
I have also drawn attention to the fact that the vagus can produce
an apparent standstill by the reduction of the contractions of the auricle
to the point of invisibility. Further, it was pointed out that the vagus
caused the ventricle to beat for a time synchronously with every con-
traction of the auricles when in consequence of the tightness of the
clamp in the auriculo-ventricular groove, or by heating the auricles and
sinus without heating the ventricle, it was beating after every second
auricular contraction or else was absolutely quiescent while the auricle
still continued beating. The reverse effect to this was also seen, the
ventricle responded to fewer auricular contractions, or in other cases
the apex of the ventricle responded to fewer base contractions during the
stimulation than before. So too when the ventricle was beating with
alternately weak and strong contractions, the vagus removed this
alternation during the time when it augmented the force of the con-
tractions, and when it was previously not present caused it to appear

^ Sokoloff and Luchsinger. PflUger’s ArcMv, Vol. xxvi. p. 4G4.

“ See abstract in Proc. Boy. Soc. Vol. xxxiii. p. 199. Full paper in Phil. Tram. 1882,
Pt. III.

* Pfliiger’s ArcMv, Vol. ix. p. 83.

S2

W. IL OASKELL.

during the time of stimulation coinciclently witli the diminution of the
force of the contractions. Assuming, as I did in that paper, that the
auricular and ventricular contractions were due to impulses proceeding
from certain motor nerve centres I imagined that these experiments
proved that the vagus had the power of both diminishing and increasing
the excitability of the ventricular muscle. Subsequently however’ my
experiments on the tortoise convinced me that such an interpretation
was erroneous, and that in reality both sets of phenomena were proofs
that the vagus was able to diminish and to restore the conduction power
of the auricular as well as of the ventricular muscular tissue. Finally it
was shown that the vagus was able to diminish the tonicity of the cardiac
muscle even when the rate of rhythm was unaltered, but that any
evidence of an increase of tone was doubtful.

For the investigation of the action of the cardiac nerves, as well as
for the study of the rhythm of the heart, the tortoise offers special
facilities over the frog. Not only is the heart more adapted for manipu-
lation owing to its greater size and the external position of its intra-
cardiac nerves, but it is specially suitable for the examination of the
vagus action owing to the presence of the coronary nerve, I propose,
therefore, to examine in order, the effect of the stimulation of the cardiac
nerves upon the rhythm, the force of the contractions, the conduction
power, and the sequence of the contractions, and afterwards to combine
the results of my experiments on the frog with those on the tortoise,
and see to what conclusions they lead.

On the action of the vagus nerves on the rhythm of the tortoise heaH,
tuhether that rhythm originates in the sinus or in other parts of
the heart.

The results of stimulation of the vagus nerves upon the suspended
tortoise heart are very much more constant than in the case of the frog
or toad. Standstill can always be obtained, whatever may be the time
of year, when the right vagus is stimulated. And though the standstill
is frequently followed by acceleration, in no case have I seen any
evidence of primary acceleration. The left vagus is much less effective
on the rhythm than the right. As a rule the same strength of stunula-
tion which when applied to the right nerve produces marked slowing or
absolute standstill, is without effect on the left nerve as far as the
rhythm is conccnrcd. With a stronger stimulation the left nerve very

1 This Jourual, Vol. ni. p. 309.

INNERVATION OF THE HEART.

83

often causes a distinct slowing which seldom if ever reaches absolute
standstill ; in many cases even when the stimulation is very strong the
rate remains absolutely unaltered. This distinction between the right
and left nerves of the common tortoise, obtainable in England {Testudo
Grceca), is evidently of the same nature as that observed by A. B. Meyer ‘
in another species (Emys Lutaria), in which the left vagus was entirely
unable to affect the rate of rhythm, and shows distinctly that only a
certain number of the nerve fibres which are contained in the two vagi
nerves have any direct influence upon the rhythm, or according to the
view already put forward, the nerve fibres supplying those mus-
cular fibres of the sinus which by their automatic contrac-
tions originate the rhythmical beats of the heart run almost
exclusively in the right vagus nerve.

When the heart is slowed or reduced to standstill by stimulation of
the vagus this slowing is often followed by distinct acceleration. The
maximum increase of rate during this after-acceleration is as a rule
much less marked than in the case of the frog, but on the other hand
the quicker rate lasts 3 much longer time. The maximum of this rate
cannot be increased by repeated stimulations of the nerve, so that it
frequently happens that the first stimulation alone produces any
after-acceleration, the subsequent stimulations serving only to make
that quicker rate more permanent, and not being able therefore to
produce any after-acceleration themselves. The after-acceleration is
most evident when the heart is beating slowly, and indeed in most
cases where the heart is beating fairly rapidly when first suspended, the
augmentative effects due to the stimulation of the nerve are manifested
not so much by any distinct acceleration as by the maintenance of the
original rate of rhythm. When the heart is left to itself the rate
of rhythm very slowly and gradually diminishes as is seen in Plate II.,
Fig. 2. ■

Further, the existence of the coronary nerve in the tortoise gives us
an excellent opportunity of determining whether the intra-cardiac nerve
trunks between the sinus and the ventricle are able to influence the
rate of rhythm or not. As has been already mentioned no effect what-
ever is produced by its section. If it be cut close to the sinus and its
peripheral end^ stimulated, the rate of beat continues absolutely the
same, it is impossible by any strength of stimulus to alter the rate of

* Ilemmunggnerven System des Herzens. Berlin, 18G9.

* By the peripheral end I mean the end in connection with the ventricle ; hy the central
end, the end connected with the sinus.

84

W. II. GASKELL.

tlie sinus rhythm by stimulating nerve fibres which are no longer in
direct connection with the sinus but only with the auricles and ventricle
through the auriculo-ventricular ganglia. In Fig. 5, PI. IV., I give a
typical example of the effect of stimulation of the right vagus, the left
vagus and the peripheral end of the coronary nerve ; in all three
cases both the strength and the length of the stimulation was the
same.

On the other hand, if the coronary nerve be cut close to its en-
trance into the auriculo-ventricular groove and the central end stimu-
lated, then in most cases a decided slowing of the rate takes place.
In Fig. 6, PI. III., I give two consecutive stimulations of the central
end of the coronary nerve. As is seen the stronger stimulation slowed
the rhythm most decidedly, while the weaker one produced no effect on
the rate of the contractions, but only upon their force. In all cases in
which I have obtained decided slowing upon stimulation of the central
end of the coronary nerve, the effect has only been produced with a
fairly strong stimulus, so that doubts arise in my mind whether such
slowing was not in reality due to escape of current, owing to the short-
ness of the nerve. I am however inclined on the whole, for the following
reasons, to think that the effect was truly due to nervous infi.uence. If
the auricles be cut away from the ventricle without cutting the coronary
nerve and vein, then the ventricle and the end of the coronary nerve
which is in connection with the auriculo-ventricular groove will in a
large tortoise be some distance away from the sinus, so that if one
electrode be placed on the ventricle, and the other on the coronary
nerve just at its entrance into the ventricle, the electrodes ■null be well
removed from the sinus, and yet in this case the stimulation of the
nerve is still able to cause slowing. Also it happens occasionally that
the free coronary vein is not accompanied by any nerve, or at all events
only a very insignificant bx’anch ; stimulation of the vein in these
circurnstances whether of the central or the periixheral end does not
produce the slightest effect either upon the rate of rhythm or the force
of the auricular contractions, even with a much stronger current than
is necessary to produce slowing when a well defined nerve is present.
Finally, as will be proved in the next section, it is clear that impulses
can pass from the ventricle to the sinus, which are able to influence the
contractions of the aui’icular muscle, and therefore it is highly probable
that similar nervous aiuangements should exist for the regulation of the
rhythmical contractions of the sinus muscle.

Combining the results of these experiments with the conclusions of

INNERVxiTION OF THE HEART.

85

Part I. of this paper, wo see that the rate of the automatic rhythmical
contractions of the muscular tissue of the sinus are regulated by
nervous impulses which pass centrifugally to the sinus from the central
nervous system, or centripetally from the other parts of the heart. The
muscular tissue of the sinus however is not the only rhythmical tissue
of the heart ; when the sinus is removed regular contraction waves still
pass over the heart which originate from that part of the remaining
muscular tissue which possesses the greatest rhythmical power. It is
then of great interest to see whether the vagus possesses the same power
of inhibiting the rhythm when that rhythm is no longer associated
with the sinus, but originates in the muscular tissue of the junction
wall between the auricles or in the auriculo-ventricular ring. Such an
investigation is rendered possible in the tortoise by the presence of the
coronary nerve. If the auricle be attached to the upper lever, the
ventricle to the lower, and the sinus be separated from the auricle by a
section which does not include the coronary nerve, then the auricle and
ventricle are connected with the body of the animal by the coronary
nerve alone, and stimulation of the right vagus in the neck can affect
their contractions only by nervous action through the coronary nerve.
As has been already explained the isolated auricle and ventricle will
after a longer or shorter pause commence to beat entirely independently
of the sinus, slowly at first, and finally more quickly and with great
regularity. When this independent auriculo-ventricular rhythm has
become regular the right vagus can be stimulated and any alteration of
rhjqhm observed as easily as in the whole heart. In PI. III., Fig. 7,
I give an example of the commonest effect produced, the whole action
of the nerve is upon the force of the auricular contractions, the rhythm
remains unaltered, although at the same time the sinus rate was
absolutely inhibited. In the preliminary communication to this paper ‘
I have stated that the rate of this independent rhythm is never affected
by stimulation of the right vagus in the neck. At that time I had
only made very few experiments of this kind, and in none of them had
I seen any alteration of rhythm. Since then however I have again
repeated this experiment, and in one case obtained most marked
evidence of complete inhibition of this independent auriculo-ventri-
cular rhythm with every stimulation of the right vagus nerve in the
neck. During the whole time of the stimulation of the nerve the
rhythm ceased entirely, and that this was no chance occurrence was

* hoc. cit.

86

W. II. GA8KELL.

seen from the fact that it occurred witli certainty with every stimula-
tion of the nerve, and never at other times, I had previously noticed
that direct stimulation of the coronary nerve was apparently sometimes
able to slow, sometimes to quicken this independent rhythm to a slight
extent, but as it was possible that this effect might be due to escape of
current owing to the shortness of the nerve, I was un-willing to accept
it as evidence of nervous action upon this rhythm, unless it were con-
firmed by similar results following upon the stimulation of the right
vagus in the neck, when the coronary nerve was the only means of
communication left between the vagus and the auricle and ventricle.
Although up to the present time I have only seen one manifest instance
of inhibition of this rhythm upon stimulation of the vagus nerve in the
neck, yet in niy opinion that one instance of positive action outweighs
all the simply negative experiments ; for it is not easy to explain this
particular marked case of inhibition if it were not due to nervous
action, while it is easy to see how the rhythm might remain unaffected,
even though the stimulation of the nerve was effective in other ways
such as in influencing the force of the am'icular contractions. In all
probability the explanation is simply as follows : When the coronary
nerve happens to contain fibres which supply the particular muscles
which originate the independent rhythm, then stimulation of the vagus
can inhibit that rhythm ; in the opposite case the rhythm is unaffected
just as Meyer found for the sinus when the left nerve of certain tortoises
was stimulated. When therefore we consider that the coronary nerve is
only one of various nerve trunks which pass from the sinus to the
ventricle, and that the auriculo-ventricular rh}frhm which arises after
removal of the sinus starts from different places in the junction wall
between the two auricles or in the auriculo-ventricular muscular ring,
according to the situation of the section by which the sinus is removed,
the probability is great that the automatic rhythm of all parts of the
heart can be inhibited by the vagus nerves, when those nerve fibres are
stimulated which supply directly the muscular fibres upon which the
automatic rhythm in question depends.

Further, experiment proves that the vagus possesses no power indi-
rectly over this rhythm. If the auricle be slit up as described in Part
II., so that all the nerve trunks between sinus and ventricle are cut, and
yet the slit has not been earned far enough to cause a block in the
auricular contraction wave ; and if from any cause, such as the flow of
blood through the coronary vessels, an independent ventricular rhj"thm
has been set up, that rhythm remains latent, and cannot make itself

INNERVATION OF THE HEART.

87

apparent, because the ventricle is compelled to contract in due sequence
with the more rapid contractions emanating from the sinus. When
however the right vagus is stimulated and a standstill of the sinus is
thus produced, then during this standstill the independent ventricular
contractions are able to appear, and are sometimes followed, sometimes
preceded, by an auricular contraction. The effect of the nerve stimula-
tion is therefore to bring to light the hidden independent ventricular
rhythm which it is unable to inhibit, although it is able to affect the
force of the auricular contractions which accompany it. That these
beats are clearly due to the unmasking of a concealed rhythm which has
been developed at the auriculo-ventricular junction by the action of the
pressure of blood in the coronary vessels is made very evident by the
simple device of slitting the auricle still more until a complete block is
caused, or by cutting away the ventricle with its part of the auricle from
the sinus. It is then found that the ventricle is beating at the rate
which was disclosed during the last stimulation of the vagus, and that
stimulation of the nerve causes now an absolute standstill of the sinus
and of the part of the auricle in connection with it. Occasionally I have
noticed the same manifestation of a ventricular rhythm during vagus
standstill, when the main nerves passing from the sinus to the ventricle
have not been previously cut. In these cases there has always been
some external cause for the development of this ventricular rhythm,
such as the presence of the clamp in the auriculo-ventricular groove,
which may have been sufficient to prevent any inhibitory action of the
cardiac nerves upon this rhythm. In the following case, each successive
stimulation of the right vagus brought to view the successive stages of
the development of this hidden ventricular rhythm in the neatest
manner.

Feb. 13, 1882. Plate IV., Fig. 8, curves i. — v. The heart was suspended
and held by a clamp placed in the auriculo-ventricular groove and screwed
tight enough to hold the tissue without preventing the due sequence of the
ventricular upon the auricular beats. The right vagus was then stimulated

at different intervals throughout the experiment. Curves i. v. represent the

effects of the several stunulations. As is seen the nerve in no case caused
complete standstill and with each successive stimulus a greater number of
regular contractions occurred during the stimulation. In Gvevy case these
contractions passed in the reverse direction, the vents'icle contracted first and the
auricle followed. In the figures the arrow with the letters V. A indicates
where this reversal began and the arrow with the letters A. V indicates the
point of return to the normal direction of the sequence. Tlie gradual and

8S

W. II. GAHKELL.

regular increase in tlio rate of tliese V. A contractions thus brought to light
is exactly similar to the development of the rhythm in the isolated ventricle
or auricle and shows that such a development was going on during the whole
time of the experiment. When the ventricle was isolated by clamping and
section it was found to be beating with great regularity at tlie same rate as
during the last vagus stimulation in curve v.

In tliese cases the independent rhythm of the ventricle was at no time
quicker than the rhythm of the sinus, and therefore was entirely con-
cealed untU the sinus rhythm was brought to a standstill by the action
of the vagus nerve. If however after section of the coronary veins
the rhythm of the sinus be artificially slowed by the application of cold
salt solution, while that of the ventricle is at the same time developed
and quickened by sending a warm blood solution through its coronary
vessels, then as soon as the ventricular rhythm reaches a rate quicker
than that of the sinus, the latter is concealed by the quicker ventricular
rh)d,hm, and we have the phenomenon of a regularly heating heart, in
which every contraction starts from the ventricle and passes through
the auricle to the sinus. Upon then cutting away the ventricle, the
slow sinus rhythm is immediately manifested. Thus the automatic
sinus rhythm can he obscured by a quicker ventricular rhythm just as
the automatic ventricular rhjThm can be obscured by a quicker sinus
rhythm.

On the action of the cardiac nerves upon the force of the contractions
of the auricle, ventricle, and sinus.

According to the principles previously laid down, we have already
examined the action of the cardiac nerves upon one of the properties of
the cardiac muscular tissue, viz. the property of rhythm, and have
therefore confined our attention exclusively to the relation of the cardiac
nerves with those particular portions of the cardiac muscle in which the
rhythmical power has been preeminently developed. We have now to
consider seriatim the action of the nerves upon the other properties of
the cardiac muscular tissues, and in the first place their action upon
the contraction force. The movements of the upper and lower levers
register the contractions of the whole auricle and ventricle, i.e. the con-
tractions of the reticulated fibres of these two cavities which form by
far the largest mass of muscular fibres. In considering, then, the varia-
tions of contraction force i^roduced by nervous action, we are essentially
considering the relations of the cai'diac nerves, in one respect at all
events, to a group of muscle fibres different in anmigcment and charac-

INNERVATION OF THE HEART.

89

ter to those which were treated of when the action of the nerves upon
rhythm was discussed.

In the course of the last year I have accumulated a large number
of curves illustrating different experiments on the heart of the tortoise,
and as the greater number of experiments commenced with the stimu-
lation of the right and left vagus nerves, and in many cases of the
coronary nerve as well, I am enabled to compare the action of the three
nerves in a large number of cases. In all cases the result of stimulation
is wonderfully constant, and is well represented in Fig. 5, PI. III.

a. In all cases the auricular contractions only are affected by the
stimulation, the ventricular contractions are never directly influenced in
the slightest degree.

h. The contractions of the auricle are always markedly diminished
in strength during the stimulation of the nerves.

c. The contractions of the auricle are increased in strength after
the end of the stimulation.

a. The strength of the ventricular contractions is uninfluenced by the
stimulation of the nerves. The contractions of the ventricle are affected
simply by the alteration of rhythm produced by the stimulation of the
nerve. It must always be borne in mind that the force of the contrac-
tion of the cardiac muscle, whether of the ventricle or of the auricle,
varies inversely as the rate of the contractions up to of course a certain
limit. The normal rate of heart beat, whether in the frog or the tor-
toise, is quicker than the rate at which the maximum contractions
would be produced. In consequence, any slowing of the rhythm will
necessarily of itself produce contractions of greater strength than the.
normal, and any increase of rate will diminish the force of the contrac-
tions in due proportion. Such an alteration in force is the sole variation
which the ventricle exhibits when the cardiac nerves are stimulated.
Thus the contractions are greater when the right vagus is stimulated in
strict accordance with the extent of the slowing produced by that
stimulation j they are absolutely unaltered when the coronary nerve is
stimulated because that nerve does not afiect the rate ; they are either
unaltered or increased in force when the left vagus is excited according
as the nerve is without effect upon or somewhat slows the rhythm.
During the after-acceleration, which is sometimes fairly well marked,
they are diminished in size in proportion to the extent of the accelera-
tion. In no case have I seen any evidence that the cardiac nerves have
the slightest power over the force of the contractions of the ventricular
muscle.

90

W. II. GASKELL.

When we compai'e the curves illustrating the action of the nerves
on the contractions of the frog’s ventricle ‘ with those obtained from the
tortoise, the absolute indifference displayed by the ventricle of the latter
to all nei’vous action becomes most puzzling and most astounding. That
the vagus should have the same action upon the strength of the contrac-
tions of the frog’s auricle, the frog’s ventricle, and the tortoise auricle,
and yet be powerless to affect the contractions of the tortoise ventricle,
leads instantly to the examination of the differences between the ventricle
of the frog and of the tortoise, which are likely to be the cause of the
marked contrast in the behaviour of the two hearts. My attention was
naturally directed in the first place to the coronary system possessed by
the ventricle of the tortoise. Bro wn-Sequard long ago suggested that
the vagus was the vaso-motor nerve of the heart, and it was therefore
possible that the force of the contractions of the ventricle of the tortoise
might be regulated by the dilating or constricting action of the vagus
nerves upon the coronary vessels ; this seemed especially probable when,
as already mentioned, it was found that the force of the contractions of
the ventricle, as well as the rate of its automatic rhythm, varied directly
with the pressure of the blood in the coronary arteries. Naturally such
an influence if present would not be manifested in the bloodless heart
cut out of the body and suspended according to my usual method.
I therefore examined the action of the vagi nerves when the circulation
was intact, and also when an artificial circulation was passing through
the coronary system of the ventricle. The contractions of the ventricle
and auricle can be registered by my method just as easily when the
heart is left in situ within the body as when it is cut out and suspended.
A thread is attached to the apex of the ventricle and to the extremity
of a thin rod fixed fiiTuly at right angles to the lever near its fulcrum.
When the lever is horizontal and placed over the body of the animal,
this rod projects vertically downwards so that the thread between the
apex and the extremity of the rod is horizontal, and the ventricle there-
fore is not pulled out of its normal position. By this means the con-
tractions of the ventricle are registered by the movements of the lever
in a vertical jjlane in precisely the same way as in the suspended heart.
In the suspended heart the fixed point between the auricles and ven-
tricle necessary for the registration of their separate contractions is
obtained by the use of the clamp or by holding the aortic trunk firmly.
In the heart with the blood flowing through it in the body I hold the

’ P/a7. Trans. 1882, Tt. iii.

INNERVATION OF THE HEART.

91

aorta firm by passing a thread partly through the thickness of its walls
and then tying it tightly to the extremity of a fixed rod which touches
the aorta at that point. Under these circumstances stimulation of the
vagus produced precisely the same curves as in the suspended heart ;
the force of the ventriciilar contractions varied with the rate only and
was entirely uninfluenced by the action of the nerve. Fig. 9, PI. III.
The same negative result followed when in the suspended heart an arti-
ficial blood solution was allowed to flow through the coronary system of
the ventricle under a constant pressure. In this series of experiments
either a slit was made in the bulged portion of the auricle in order to
prevent the distension of the heart cavities with blood, or the auricles
were entirely removed with the exception of the junction wall along
which the nerve trunks pass to the ventricle ; or the coronary nerve
alone was left as the means of communication between the ventricle and
the sinus. In none of the curves, howevet, whether the pressure in the
coronary system was small or great, whether the ventricle was beating
in response to the auricles or with its own independent rhythm, was
there any evidence that the vagus nerves are able to influence the force
of the ventricular contractions. We must then seek for some other
cause than the presence of a coronary system in order to account for the
indifference of the muscular tissue of the tortoise ventricle to vagus
stimulation.

h. The contractions of the awicle are diminished in strength during
the stimulation of the nerves. All three nerves act in the same man-
ner upon the contractions of the auricle, as is shown in Fig. 5, PI. III.
During the stimulation the contractions are most markedly diminished
in force quite independently of the action of the nerves upon the rate
of rhythm, and in fact in this respect the left vagus often appears to
possess greater power than the right. Occasionally, as mentioned in my
preliminary paper*, the right nerve loses this power to a greater or less
extent after section of the coronary nerve, although naturally its effect
upon the rate of rhythm is as powerful as ever. It is evident, then,
that those nerve fibres which supply the bulged portion of the auricles
run in both vagus nerves and pass to the auricles not only from the
nerve trunks in the sinus but also from those in the junction wall of the
auricles, even after they have reached the auriculo-ventricular groove.
These nerve fibres are in no way dependent for their action upon those
which supply the rhythmical tissue of the sinus, as is shown plainly

pr(. TV.

^ Loc. cit. p. 372.

8

92

W. H. GASKELL.

enough by the similar effect produced by the right, left, and coronary
nerves, and still further by the action of the right vagus when the
coronary nerve is the only channel left by which nerve impulses can
reach the auricle. As has been already described, a regular independent
auriculo-ventricular rhythm is ultimately set up after separation of the
auricle and ventricle from the sinus. The force of these auricular con-
tractions can be diminished by stimulation of the right vagus in the
neck (the coronary nerve being left intact) without any alteration of
this rhythm, as is shown in Fig. 7, PI. III. At the same time the
sinus may be reduced to standstill. Similarly, when the auricle is slit
up so that a complete block occurs, and in consequence the sinus and
that part of the auricle which is connected with it are beating at one
rate while the ventricle and its part of the auricle are contracting inde-
pendently at another rate, then naturally stimulation of the vagi nerves
in the neck reduces only the contractions of the sinus-auricle, while
stimulation of the peripheral end of the coronary nerve reduces only
those of the ventricle-auricle.

Again, stimulation of the central end of the coronary nerve may not
only slow the rhythm but also diminish the force of the auricular con-
tractions ; that this result is not due to escape of current is shown by
the effect of stimulating the surface of the ventricle when the coronary
nerve is the only channel of communication between the ventricle and
the sinus. In this case the amdcle is left in connection mth the sinus
and the electrodes placed on the surface of the ventricle at different
distances from the auriculo-ventricular groove and the entrance of the
coronary nerve into that gi’oove. At distances from one to two centi-
metres from the point of entrance to the nerve in the neighbourhood of
the base of the ventricle, a decided diminution in the force of the
auricular contractions without any alteration of rhythm may be jaroduced
when an interrupted current is sent through the small portion of the
surface of the ventricle between the electrodes ; and indeed I have seen
this effect plainly manifested when the current was so weak that
no contraction of the ventricle was caused by it. It would
seem therefore that in the tortoise the cardiac nerves have no power
over the force of the ventricular contractions, but that nervous arrange-
ments exist by means of which the ventricle is able to regulate the force
of the auricular contractions as well as in all probability the rate of
rhythm. It is then conceivable that the function of many of the nen^e
fibres which pass into the ventricle is, by their action upon the force of
the auricular contractions, to regulate tlie amount of blood thrown into

INNERVATION OF THE HEART.

98

the ventricle and therefore the amount of work done by the heart.
The nervous arrangements of the tortoise heart seem thus to bear out the
view put forward by Roy‘ that the work of the heart is governed chiefly
by the contraction of the auricle.

In speaking of the action of the vagus upon the contractions of the
frog’s heart' I have proved that a typical inhibition is often brought
about ■without any alteration of rhythm by the diminution of the auri-
cular contractions to the point of invisibility, a form of standstill described
subsequently by Heidenhain*. In the tortoise I have never yet seen
such a complete obliteration of the contractions of the auricle ; although
they may be very greatly reduced in force yet they are always visibly
registered. Again, another point of some interest is noticeable in all
those curves where the stimulation of the nerve has produced standstill.
The first auricular contraction after the standstill is somewhat larger
than the contractions immediately following it, although considerably
smaller than the contractions before the commencement of the stimula-
tion. This is well shown in Fig. 14, PI. IV., and is clearly due to the
antagonism between the augmenting effect of a longer pause and the
diminishing effect of the action of the nerve.

Finally the contractions of the sinus are diminished in force similarly
to those of the auricle, when the vagus nerves are stimulated.

c. After the end of the stimulation the contractions of the auricle
are increased in strength. Here again, just as in the case of the rhythm,
the augmentation effects consequent upon nerve stimulation are much
less marked than in the frog’s heart. In the latter the maximum
increase in the strength of the contractions is rapidly attained and its
extent is often very great ; in the tortoise the increase of the auricular
contractions after each stimulation is very slight but lasts over a long
period of time, so that in the course of each experiment, when the vagus
nerves have been stimulated many times, the net result upon the auri-
cular contractions is a very marked increase in their strength. That
such an increase is truly due to the action of the nerves and would not
have occurred otherwise, is shown by experiments similar to that
de.scribed on p. 57, where the contractions of aiu'icle and ventricle were
registered for many hours without any stimulation of nerves, and it was
seen that the auricular contractions did not increase in strength from

‘ This Journal, Vol. i. p. 495.

* Op. cit. See also Tmtui. of the Inlemat. Med. Congress, London, 1S81. Vol. i. p.257.

* Pfliiger’s Archiv, Vol. xxvn. p. 383.

8--2

9-i

W. II. QAHKELL.

the time of suspension onwards, but on the contrary, gradually steadily
and persistently became smaller and smaller.

This slow, gradual, and permanent improvement in the force of the
auricular contractions is manifest after the stimulation of either the
right vagus, the left vagus, or the coronary nerve ; in fact, just as all
three nerves are able to diminish the strength of the contractions, so
also are they able afterwards to increase that strength. Fig. 5, PI. III.
Here also as in the frog, toad, and rabbit the augmentation effects
produced by the vagus are most manifest when the heart is beating
weakly. The following example illustrates both the extent and the
permanence of the augmentative effects of the nerve stimulation upon
both the rate of rhythm and the strength of the contractions.

Feb. 7, 1882. The heart was held by the clamp in the auriculo-
ventricular groove so slightly that the ventricle was able to respond to every
auricular contraction. The auricle was fixed to the upper, the ventricle to
the lower lever. The tracings were made upon the blackened paper of a
drum which completed one revolution in 12 minutes. The first five tracings
were taken without any alteration in the conditions of the experiment, so
that allowing for the time of changing drums, pauses purposely made during
the experiment, &c., the fifth tracing was made at least 1^ hours after the
commencement of the first.

Eate

Height

per min.

in mm.

At the commencement of curve i.

7-75

22-5 1

1 R. vagus was .stimrilated

At the end of curve i.

8T5

25-5 J

1 once during this curve.

At the commencement of curve ii.

?

26-5 ^

j L. nerve twice stimulated

At the end of curve ii.

8

30

1 during this curva

At the commencement of curve iii.

7-75

33 \

R. vagus twice stimu-

At the end of curve iil.

9-25

36-5 J

lated.

At the commencement of curve iv.

8-5

38 j

R. vagus twice stimu-

At the end of curve iv.

9-5

38-5 J

lated.

At the commencement of curve v.

8-25

38-5

As is seen the strength of the contractions increased steadily after every
stimulation whether of the right or left nerve, so that in less than 1^ hours
the height of contraction had increased to the extent of f of the original
height.

On the action of the cardiac nerves upon the conduction power of

the auricidar muscle.

The reticulated fibres of the auricle not only contract with a certain
degree of force, but their contraction takes place in the shape of a wave

INNERVATION OF THE HEART.

95

which passes fi'om the sinus end over the whole network of fibres to
their termination in the auriculo-ventricular muscular ring. The power
of the muscular tissue to conduct this wave of contraction is clearly
as likely to be influenced by the cardiac nerves as the force of the
contraction itself ; and in fact, experiment proves that the right vagus,
the left vagus, and the coronary nerve, all possess an influence over the
conduction power, just as we have already seen that they are all able to
influence the force of the contractions. In all probability then, the nerve
fibres which supply the reticulated muscle fibres of the auricle produce
changes which affect both the force of the contractions and the power
of conduction.

When the auricle is slit up to a sufficient extent a partial block is
always produced, such that only every second contraction which is started
from the sinus end passes over the block and produces a ventricular
contraction. This is the condition which is most favourable for deter-
mining the action of the cardiac nerves upon the conduction power,
because it represents a condition intermediate between the two extremes
of a complete block and no block at all; we can therefore study the
variations in both directions. Evidently such a partial block may be
increased by the action of the nerves and therefore only every third,
fourth, &c. contraction be able to pass, or on the other hand the conduc-.
tion power may be improved and then every contraction will be able to
pass. By careful manipulation the right amount of section necessary
for the production of such a partial block is always attainable, and indeed
this condition can be reproduced at will again and again in the course
of a single experiment. I have already shown how, in the case of the
frog, tightening of the clamp in the auriculo-ventricular groove produces
a partial block, permitting only every second contraction to pass, and
that this may last a considerable time or may give way to a complete
synchronism of the auricular and ventricular contractions. In exactly
the same way such a partial block of the auricular contraction wave in
the tortoise lasts sometimes a long time without alteration, at other
times lasts only a short time and then every contraction passes over.
The application of 075 p.c. solution of salt to the blocking point is very
efficacious in removing this partial block and causing every contraction
wave to pass over, and then by simply drying Avith a piece of blotting
paper the block can be brought back and again only every second
contraction will pass. In this way by alternately moistening and dry-
ing the blocking point I have been enabled to see again and again
in the course of an experiment the formation and disappearance of such

9G

W. II. 0 ASK ELL.

a partial block. Hence it is necessary to be careful that any apparent
removal of such a block by nervous action is not in reality due to a
chance removal of the block coinciding -with the time of the nerve
stimulation. As a matter of fact such an explanation is out of the
question; the large number of curves which I possess show that the
coronary nerve as well as the right and left vagus possess the power of
removing a partial block as conclusively as my former curves show the
same power in the vagus nerves of the frog. Again and again by care-
ful section I have caused a partial block and watched for a long time
the regular passage of every second contraction, and then after stimu-
lation of one of the three nerves seen every contraction pass (see Figs.
ID, 11, PI. IV.). This improvement of conduction power is, like the im-
provement in the force of the contractions or the after-acceleration, spread
over a long period of time, so that in most cases stimulation of the nerve
removes the partial block altogether, and every contraction continues
to pass with absolute regularity until by drying or further section
the partial block is brought back. In the frog, on the other hand, as
has been shown in my former paper, the restoration of the conduction
power in consequence of nerve stimulation is not so lasting. Occasion-
ally (see Fig. 10, PI. IV.) stimulation of the vagus or the coronary nerve
in the tortoise improves the conduction power for only a limited time
after the stimulation, so that in these cases there can be no question as
to the influence of the nerve ; every second contraction passes before
the stimulation, then during and after the nerve stimulation every
contraction passes, and then again in a very short time only every
second contraction is able to pass. It does not seem to make any
difference whether the nerve influence reaches the blocking point from
the ventricular side or from the sinus side, whether therefore the coro-
nary nerve or the right or left vagus nerves be stimulated. Some-
times the conduction power is most easily restored by the coronary
nerve, sometimes by the right or left vagus, and as a rale one nerve may
be more efficient than the other two. Doubtless such differences are
due to differences in the arrangement of the neiwe fibres in each
particular case, as well as to the exact position of the section bj' which
the ]3artial block was caused.

In the frog experimental evidence showed that nerve stimulation
much ofteuer removed than increased a block in the contraction wave ;
so too with the tortoise, I possess but few curves which show unmistake-
ably any diminution of conduction power in consequence of nerve
stimulation. Still, as Figs. 12, 13, PI. IV. show, such an increase in the

INNERVATION OF THE HEART.

97

extent of tlie block does undoubtedly sometimes occur. In these cases
eveiy second contraction was passing before stimulation of the right
vagus and coronary nerves respectively, and during the stimulation
every contraction failed to pass.

We may then say that both in the tortoise and in the frog the
cardiac nerves are able both to depress and exalt the conduc-
tion power of the muscular tissue of the auricle. The nature
of this nerve action can only be examined after an answer has been
given to the question, Under what conditions can a partial block be
caused of such a character that only every second contraction wave
passes the block? If the sinus and its connections with the auricle be
removed and single induction shocks be sent through the sinus end of
As at regular intervals, so as to cause a regular series of artificial con-
traction waves, it is found that —

1. Variations in the strength of the stimiilus have no effect upon
the passage of the contraction wave over the block. If a contraction
wave can pass at all, it will pass as well when caused by a weak as by a
strong stimulus; if it cannot pass with a weak stimulus, it will not
■ivith a stronger one.

2. Two consecutive contractions cannot pass the block unless a
sufficient time elapse between the contractions. Thus with single
induction shocks every ten seconds all the contractions will pass or will
not pass according to the extent of the section ; but with the same
severity of section when all contractions at ten seconds intervals are
able to pass, it is possible that with single induction shocks every five
seconds only every second contraction will pass. So too with a section
such that all contractions at five seconds intervals can pass, it is possible
that with three seconds intervals only every second contraction will
pass.

Now we know fi-om the experiments of Marey that a certain time
must elapse after a contraction before the cardiac muscle is in a con-
dition to contract again ; in other words, the muscle takes time to re-
cover its full excitability after a contraction. The same law applies
to every portion of a cardiac muscle along which a wave of contraction
travels, and we may therefore say that a certain time must elapse after
a wave of contraction has passed over the muscle before the conduction
power is sufficiently re-established to allow the passage of a second
contraction wave. The effect then of the injury caused by the section
together with the narrowing of the path of conduction is to retard this
process of re-establishment of the conducting power; in consequence

98

W. II. G ASK ELL.

a still longer time must elapse after a contraction wave has passed,
before the tissue at the blocking point has recovered sufficiently to
allow a second contraction to pass.

Nervous action therefore removes a partial block, and
enables every contraction to pass the blocking point because
it expedites the recovery of the conduction power of the
muscle at that point: a recovery which without the stimu-
lation of the nerve would take place more slowly after the
passage of each contraction wave.

This repau’ of conduction power due to nerve action is apparently
independent of the action of the nerves upon the force of the auricular
contractions. When a partial block has been caused, so that every
second contraction passes, and the right vagus nerve is stimulated, it
frequently happens that from the commencement of the stimulation
every contraction passes the block, although during the stimulation
the force of the contractions of the sinus-auricle at all events is very
markedly reduced. Since, however, this diminution is always accom-
panied with considerable slowing, it is possible that in this case every
contraction passes the block, even when the force of the contractions
is reduced, because a sufficient length of time elapses between con-
secutive contractions; and indeed, in those cases in which nerve stimula-
tion has caused a distinct increase in the block, whether the nerve
in question be the right vagus, left vagus, or coronary, the rate of
the contractions has never been appreciably slowed. Such an explana-
tion however will not hold good in those cases, where hy stimulation
of the coronary nerve or the left vagus the force of the contractions
is markedly reduced while the rate is left unaltered. In both these
cases the force of the contractions may be markedly diminished and
at the same time the conduction power as markedly increased, so that
during the stimulation every contraction is able to pass, although before
the beginning of the stimulation only every second contraction was
passing. The evidence then goes to show that the same nerve may
produce both an increase or a diminution of the conduction
power of the auricular muscle simultaneously with a di-
minution of the force of its contractions.

Finally, I have shown that in the frog and toad the stunulation
of the vagus is able to make the ventricle resjDond for a time to every
contraction of the auricles, even when in consequence of the tightening
of the clamp in the auriculo-ventricvdar groove or of the application
of heat to the auricles and sinus alone, it was unable to rcsjiond to

INNERVATION OF THE HEART.

99

auy single auricular contraction before the stimulation of the nerve.
In other words, the vagus was able temporarily to remove a complete
block in the passage of the contraction wave from auricle to ventricle.
In the tortoise also it is possible to restore the conduction power by
nerve stimulation even when the block is apparently complete. Natu-
rally it is not easy to make sure of success in such an experiment every
time, for, if the section of the auricle be carried slightly too far, the
block will be complete enough but the vagus will be unable to repair
it. It is however possible to cut the auricle just sufficiently to prevent
the passage of any contractions to the ventricle ; if the nerve then
be stimulated contractions immediately begin to pass the block, and
increase rapidly in number, until a short time after the stimulation the
conduction power is so fully restored that every contraction passes the
blocking point, and a new cut must be made in order again to block
the passage of the contraction wave.

On the action of the cardiac nerves upon the sequence of the contrac-
tions of the different heart cavities.

It has already been argued that the natural pauses between the
contractions of the different heart cavities, and therefore the normal
sequence of those contractions, is a consequence of an alteration of
conduction power which occurs normally as the contraction wave passes
from the sinus to the auricles, or from the auricles to the ventricle
respectively. It is extremely likely then, that the cardiac nerves should
be able to influence the passage of the contraction wave at these
natural blocking points, in the same manner as has just been described
in the case of an impairment of conduction produced by an artificial
block. We may therefore expect to find, that the vagus can either
increase or diminish the natural block in the same manner as it is
able to affect the artificial block. When an artificial partial block is
produced, the most striking effect of nerve stimulation is the removal
of that block and therefore the complete repair of the conduction
power , on the other hand, the most striking alteration of the nor-
mal sequence of the contractions would result not from any im-
provement but from an impairment of the conduction power. Thus,
any alteration of conduction power at the sino-auricular and auriculo-
ventricular junctions is made evident simply by a corresponding altera-
tion in the natural pause, which occurs between the contractions of the
sinus and the auricles and of the auricles and ventricle respectively ;

100

If. II. GASKELL.

any increase therefore of tlie conduction power at these junctions can
only be manifested by the contractions of the auricles and ventricle
following upon those of the sinus and auricles respectively with greater
rapidity than before, while any diminution in the conduction power may
cause either a diminution of the rapidity of the sequence or an absolute
cessation of sequence according to its extent. For this reason it is
clear that any marked increase in the natural block at these junctions
will be much more striking and apparent than an equally marked dimi-
nution of that block. Such is the case ; when the vagus nerves are
stimulated, the cessation of the sequence in consequence of the stimu-
lation is manifest enough, the recovery of the sequence is only well
marked when the natural block has been artificially increased by the
pressure of the clamp in the sino-auricular or auriculo-ventricular
grooves.

When the heart is suspended and the aorta fixed, no clamp being
used to the heart itself, the contractions of sinus, auricle and ventricle
follow one another with perfect regularity and the beats of the sinus
are often registered on the auricular curve. In many cases stimu-
lation of the right vagus stops the contractions of the auri-
cles and ventricle absolutely, while the sinus still continues
beating ; see Figs. 14, 12, PI. IV. This standstill of the auricles is not
due to a diminution of the force of the auricular contractions sufficient
to render them invisible, as was previously noticed in the case of the
frog and toad; for the sinus contractions are well marked and can
be plainly seen to stop short when they reach the sino-auricular junc-
tion; in addition it frequently happens that the block caused by the
vagus stimulation is not a com2Dlete one, so that some of the sinus
contractions are followed by contractions of the auricle ; these auricular
contractions are no smaller than is usually seen when the right vagus
is stimulated. Clearly then the passage of the contraction from sinus
to auricle may be completely or j)artially blocked during the stimula-
tion of the right vagus nerve. Such a block is entirely independent
of the effect of the nerve upon the rhythm or the contraction force
of the sinus muscle. In many cases the sinus continues to beat during
the whole of the stimulation at absolutely the same rate as before
the stimulation, in other cases the sinus rate is markedly slowed ;
and yet in both cases not a single contraction passes into the auricle.
Sometimes the sinus contractions are diminished so as to be barely
visible, at other times their force is scarcely if at all affected, and
yet the block is comjilete in both cases. A similar comjjlete cessation

101

INNERVATION OF THE HEART.

of the sequence of the auricular upon the sinus contractions during
stimulation of the vagus nerve is often seen in the snake, and to a
less extent in the frog and toad, so that a third method of producing
standstill must be ascribed to the vagus. We may have therefore stand-
still of the auricles and ventricle produced in the three following ways :

1. Cessation of rhythm.

2. Cessation of contraction.

3. Cessation of conduction.

In many cases the diminution of the conduction at the sino-
auricular junction during vagus stimulation is not sufficient to produce
a complete block, but only to lengthen the pause between the con-
tractions of the sinus and auricles. Such an increase in the natural
pause is often well marked even with the drum revolving very slowly
(once in 13 minutes), as is seen in Fig. 15, PI. V. The want of rela-
tion between the contraction force and the conduction power, which was
noticed in the case of the artificial block, is equally noticeable when
the natural sequence of the contractions is the subject of examination.
Even when stimulation of the vagus reduces the force of the con-
tractions of the auricle very greatly no sign of a block can be seen
at the auriculo-ventricular junction. The ventricle may respond with
strong vigorous contractions to each of these diminished auricular
contractions just as well as to the previous strong auricular contrac-
tions. This fact not only suggests that the conduction of the con-
traction wave from auricle to ventricle is not necessarily impaired at
the same time that the force of the auricular contractions is diminished,
but it also shows that even with a great diminution of the force of
the contractions, a contraction wave still passes from end to end of the
auricular muscle and induces a ventricular contraction, and therefore
that the diminution in force due to the vagus stimulation is not brought
about by the cutting short of the contraction wave when it had passed
only a short way along the auricle.

The improvement in conduction power at the sino-auricular and
auriculo-ventricular junctions caused by the stimulation of the vagus is
evident enough when the natural sequence is in any way hindered, so that
the ventricle is beating after every second contraction of the auricle or the
auricle is made to respond to every second sinus contraction. At both
junctions such an increased block can easily be produced by the action
of the clamp ; in both cases stimulation of the nerve is able to remove
that block and to restore the sequence in the manner described already.
In the tortoise and the frog the action ol the clamp is necessary so as to

102

W. 11. OASKllLL.

increase the natural block, in order to demonstrate the recovery of
sequence after vagus stimulation. In the heart of the common ringed
snake however no such extra assistance is required. The heart of the
snake is apparently much more suscejitible to any interference than any
other heart which I have as yet examined. It is the rule rather than
the exception to find that its mere suspension between the two levers,
when the aorta is held and no clamp is used, is sufficient to interfere
mth the due sequence of the contractions. The sinus continues to beat
■with gi'eat regularity but only a certain number of those contractions
are followed by auricular contractions, and again of these latter, some
only give rise to a contraction of the ventricle. Thus a common form of
rhythm which may last unaltered for a long time is as follows; the auricles
contract only after every second sinus contraction, and only every second
of these auricular contractions is followed by a contraction of the ven-
tricle. Thus in this case the ventricle contracts after every fourth and
the auricle after every second sinus contraction.

Stimulation of the vagus acts here in the manner already suggested ;
during the stimulation the sequence is sometimes still more hindered
than before ; the sinus alone contracts, auricle and ventricle remain still.
After the stimulation a marked improvement of the sequence often
takes place, for a time the auricle may respond to every sinus contrac-
tion, and in other cases the ventricle contracts after every auricular
contraction. In fact the action of the vagus upon the sequence is very
similar to what is seen in a frog when a clamp is placed in the auriculo-
ventricular groove. The snake’s heart not only affords a good instance
of the recovery of sequence in consequence of nerve stimulation, when
the sequence has been pre'viously irregular, but also shows the increase in
the rapidity with which the contraction of the auricle may be made to
follow that of the sinus, in a much more striking manner than I have
as yet seen in the tortoise. In Fig. 16, PI. V., the rotation of the drum
was quick and one auricle was attached to the upper lever, the ventricle
haviug been pre'viously cut away. The heart therefore remained in the
body and the contractions of both sinus and auricle wmre registered by
the same lever. As is seen, the pause between the contractions of the
sinus (S in the Fig.) and of the auricle (A) was remarkably long before
the stimulation, so that the contraction of the sinus ■«'as over before
that of the auricle began. During the stimulation the two contractions
were so close as to fuse together in the curve and then gi-adually the
pause became longer and longer until the original length of pause was
again reached. It may also be noticed that the nerve stimulation

INNERVATION OF THE HEART.

103

diminished the force of the auricular contractions to a greater extent
than those of the sinus, so that during the maximum effect the beats
of the latter were actually stronger than those of the former.

The power of the vagus nerve to hinder the sequence of ventricular
upon auricular beat has only been noticed by me, when a hindrance to
the conduction has already been caused by the presence of the clamp in
the auriculo-ventricular groove. Eckhard’s^ experiments however seem
to show clearly that the nerves of the septum in the frog are able on
stimulation to block the passage of the contraction from the auricle to
the ventricle, for he found that their stimulation caused the ventricle to
stand still while the sinus and auricles continued beating. These nerves
therefore acted upon the conduction power of the auriculo-ventricular
muscular ring in the same way as the right vagus acts on the conduction
power of the sino-auricular muscular ring in the tortoise.

On the nature of the action of the vagus nerves and its resemblance
to the action of a weak interrupted current.

A comparison of the results obtained from the tortoise with those
described in my former paper on the frog, confirms the view put forward
there that the vagus is the trophic nerve of the heart. Its action is of
the same kind throughout, and the different effects produced are not due
to the action of different nerve fibres possessing different properties, but
rather to the action of the same kind of nerve fibre upon the different
attributes of the cardiac muscular tissues. Thus the nerves supplying
the red and white muscles of rabbits are not supposed to be different to
other motor nerves, yet their stimulation produces very different results
owing to the differences which exist in the red and white muscles
themselves. In precisely the same way the same kind of nerve fibre
will produce different results in the heart according as the muscle fibres
upon which it acts are specially engaged in the initiation of rhythmical
contractions, in the conduction of a contraction wave, or in the produc-
tion of strong and rapid contraction. Thus, to give an example, we have
seen that as long as the attention is confined to the movements of the
auricle and ventricle it is possible to obtain by stimulation of the vao-us
nerve a typical inhibition which may be caused in three different ways.

1. The standstill may be due to the cessation of the rhythm, i.e. to
the depressing action of the nerve upon the rhythmical power of the
muscle fibres of the sinus (Frog, Tortoise, Snake).

Op. cit. p. 193.

1

104

W. II. GAHKELL.

2. It may be due to the diminution of the auricular contractions to
the point of invisibility, i.e. to the depressing action of the nerve ujx)n
the contraction power of the rapidly contracting reticulated muscle fibres
of the auricle (Frog).

3. It may be due to a blocking of the contraction at the sino-
auricular junction, i.e. to the depressing action of the nerve upon the
conduction power of the muscular fibres connecting the sinus and
auricle (Snake, Tortoise, Frog).

In these three cases the same practical result is brought about by in
all probability the same kind of nerve fibre influencing three of the
different attributes of cardiac muscle, viz. rhythm, contraction, and con-
duction. Again, we see that both in the frog and the tortoise the vagus
possesses the power of exalting as well as of depressing all the different •
functions exhibited by the cardiac muscles ; and it is noticeable that the
difference between the frog and the tortoise is in this respect the same
throughout. Thus : —

In the frog the augmentation of the contractions is very marked, the
maximum is quickly reached and the contractions return again to their
original size.

In the tortoise the augmentation is slight but its effect is spread
over a much longer time.

In the frog the exaltation of conduction power follows the same
limits as the augmentation of the contractions.

In the tortoise the repair of conduction power is much more per-
manent.

In the frog the acceleration is marked and does not last long.

In the tortoise it is slight but long enduring.

The exalting action of the vagus then runs a more rapid course in
the frog than in the tortoise with a corresponding greater maximum.
This is in strict accordance with the greater slo'wness of aU the normal
functions of the tortoise heart ; thus, the normal rate of rhjffhm is much
less than that of the frog, the contraction of the frog’s ventricle is more
rapid, the refractory period in the tortoise is longer than in the frog. In
other words the augmentation of function producetj by vagus stimula-
tion varies in the rate of its production and in the maximum of its effect
according to the rapidity of the normal metabolism of the tissue. If
then we combine the present observations on the tortoise with the
arguments at the end of my paper on the frjog we arrive at the following
conclusion ;

Although the initial effect of the vagus is to depress some

INNERVATION OF THE HEART.

105

function, its final and most enduring power is to exalt, inten-
sify and repair that function.

Thus, although it slows rhythm, yet its stimulation makes the
rhythmical power last longer than it otherwise would and makes the
heart beat with regularity when it was previously irregular ; although
it reduces the force of the contractions, yet its ultimate effect is to
improve and sustain the contraction force ; although it may diminish
the conduction power yet in the end it completely repairs that power.
For these reasons I look upon the vagus as essentially the
trophic nerve of the heart.

It is possible to gain some insight into the nature of this trophic
action by the examination of the behaviour of the cardiac muscle
to direct stimulation. Hitherto almost all the experiments upon the
effect of single induction shocks on the functions of the cardiac
muscle have been conducted in the manner introduced by Ludwig
and are extensions and modifications of the original experiments of
Bowditch*. His experiments combined with those of Kronecker’^ and
V. Basch^ show that —

1. The strength of the contraction of the muscular tissue of the
apex of the frog’s ventricle does not vary with the strength of the
stimulus : a minimal stimulus is at the same time maximal.

2. When the apex is made to contract regularly by sending through
single induction shocks at definite intervals, each contraction is stronger
than the previous one until a certain maximum is reached, i.e. the series
of contractions are arranged in the form of a staircase.

3. When the single induction shocks follow at a sufficiently rapid
rate, then the ventricular muscle responds, if the stimulus is weak, to
every second stimulation only, although it is able to contract with each
stimulation upon increasing the strength of the stimulus.

The explanation of § 3 is to be found in the observations of Marey,
that the refractory period of the ventricular muscle of the frog is very
long, so that the muscle recovers its excitability after a contraction quite
slowly, combined with the assertion of v. Basch, that a stimulus which
is of itself too weak to cause a contraction increases the muscular excita-
bility and therefore helps the production of a subsequent contraction.

All these laws can be studied on the muscular tissue of the apex of
the auricle of the tortoise a§ well as on that of the ventricle ; moreover,

> hudwig’ a Arbeiten, 1271. ‘

“ Dascharak. Merkmal der Ilerzmuskel Beweg. Ludwig’s Festgabe, 1874.

3 Sitzber. d. k. Akad. d. Wiss. (Wien), Bd. lxxix. III. Abth.

106

ir. II. OASKELL

it is not necessary to make use of the apex cavity or to keep it supplied
with an artificial blood solution ; a strip of muscular tissue cut from the
apex of the ventricle or auricle and suspended as above described enables
us to demonstrate all the laws of the stimulation of cardiac muscle men-
tioned above. Thus in both the strip from the tortoise’s auricle and the
frog’s ventricle a minimal stimulation is at the same time maximal, in
both a series of single stimulations produces a “ staircase,” in both the
strip contracts regularly with every second induction shock when the
stimuli are sufficiently weak and sufficiently rapid. A compaiison of
the reaction of the three muscular strips from the apex of the frog’s
ventricle, tortoise auricle and tortoise ventricle shows that with single
induction shocks of the same strength at five seconds intervals the muscle
of the frog’s ventricle and the tortoise auricle will respond to ever}'
stimulus, but that ten seconds intervals are necessary in order to make
sure of an infallible response in the case of the striji from the apex of
the tortoise ventricle.

Again Bowditch’s law of the “Treppe” is not confined to the de-
velopment of the power of contraction in the muscle, the same kind of
improvement is seen in the development of the rhythmical power. The
difference between the rhythm caused by external excitation and the
rhythm which is brought about by internal changes is that the first is
quickest at the time of excitation and dies away as the effects of the
stimulus wear off, while the second is slowest at the commencement and
steadily gains in rapidity and regularity as the automatic power is
developed. If then a series of lines were drawn inversely as the lengths
of time between the successive automatic beats, those lines would form
an ascending staircase as the rate quickened, just as the contractions
form an ascending staircase in Bowditch’s experiment. In other words,
each automatic contraction quickens the development of the next auto-
matic contraction, just as each artificial contraction increases the force of
the next succeeding artificial contraction, up to of course in each case a
maximum limit.

I have already described fully how a weak inten’upted current ajDplied
to a strip of ventricular muscle gradually improves the conduction power
and contraction force of that strip until at last automatic contractions
result. In that description I purposely said nothing about the action
of a weak interrupted current upon the auricular muscle further than
mentioning that it also could be taught to beat automatically. The
difference however between the behaviour of the strips from the auricle
of the tortoise, the ventricle of the frog and the ventricle of the tortoise

INNERVATION OF THE HEART.

107

in this respect is most striking and suggestive. In each case the
weak interrupted current affects the force of the contrac-
tions of the several strips in precisely the same manner
as the vagus nerve acts upon the whole auricle or ven-
tricle from which the strips are taken. Thus when the strip
from the apex of the frog’s ventricle is made to contract every five
seconds and the contractions are of equal height, they are immediately
diminished most markedly in force during the whole time that the weak
interrupted current is passing. After the cessation of the stimulation of
the inten-upted current the induced contractions increase most markedly
in size and I’apidly attain a maximum much greater than the original
contractions. The curves are in every respect precisely similar to those
obtained by stimulation of the vagus as given in my previous paper,
except of course that each contraction occurs at five seconds intervals.
The diminution of force may be so great that the contractions are barely
visible.

Also atropin has here the same effect upon the action
of the interrupted current as upon vagus action ; at first
after atropin has been applied to the strip, the interrupted current
still diminishes the contraction force but to a less extent than before,
afterwards no diminution occurs but a primary increase of force even
during the passage of the current, and finally the inteirupted current
is unable to influence the force of the contractions in either direction.

In a precisely similar manner an interrupted current, which is so
weak as not to cause contractions itself, diminishes the force of the
contractions of the strip of muscle from the tortoise auricle during the
passage of the current and helps on the contraction force, making the
beats more and more vigorous by the same slow sort of permanent after-
effect which has already been described as characteristic of the action of
the vagus nerves upon the contractions of the whole auricle. Again as
is shown in Fig. 17, PI. V., the same effect is produced after the strip has
been brought into the condition of automatic rhythm ; and indeed the
effect may be even more pronounced on the day after the strip was sus-
pended, when as in the instance given the automatic rhythm had con-
tinued at least 24 hours. In Fig. 17, curve ir., I give the effect of the
stimulation applied at 12.30 on the morning of Nov. 22 to the strip of
auricular muscle which had supplied curve i. on the afternoon of Nov. 21.
The secondary coil was gradually pushed from 8 to 5 cm. and the inter-
rupted current caused as is seen a single contraction with the sec. coil at
") cm. The regularity of the automatic contractions at least 24 hoiirs
PH. IV. (1

108

W. II. GASKELL.

after suspension of the strip is well shown, as well as the diminution and
after increase of force caused by the interrupted current. Here too
atropin produces the same effect as upon vagus stimulation,

A precisely similar effect, as far as the diminution of the contractions is
concerned, was observed by F oster and Dew-Smith* during the pa.s.sage
of a constant current through the muscular tissue of the frog’s ventricle,
when that ventricle was beating. The similarity between the action of
the weak intemipted current upon the contractions, whether spontan-
eous or produced by single induction shocks, with the above-mentioned
effect of the constant current, naturally leads to the suggestion that such
an effect may depend upon the polarization of the muscle by the weak
interrupted current. I have therefore placed the exciting electrodes
at the fixed upper end of the strip, at the lower end, and in the middle
of the strip, and in each of these three positions have observed the effect
upon the contractions of the interrupted current sent through the whole
strip from end to end. In each case I have also reversed the direction
of the current through the strip and varied it in strength. In all cases
the result was the same, the strength of the contractions was markedly
diminished during and slightly increased after the stimulation.

Finally, the interrupted current as already mentioned slowly causes
an improvement of contraction force and conduction power in the strip
from the tortoise ventricle, until the maximum contractions have been
reached, until the rhythmical power has been fully developed and auto-
matic contractions result. During this period of development there Ls
no marked sign of any diminution in the force of the contractions during
the passage of the interrupted current. When the strip contracts with
equal maximal contractions, when the automatic rhythm is regular the
interrupted current is still unable to influence the contraction force, at
all events to any definite extent. Sometimes the contractions do appear
to have been diminished exceedingly slightly during the passage of the
current ; especially before the force of the contractions has developed to
its full extent. Such a slight diminution may truly correspond to the
marked diminution which is brought about in the auricular muscle by
the passage of the current, but it is so insignificant and so doubtful
when the strip of muscle is contracting to its fullest extent as not to
prevent the resemblance between the action of the vagus and the inter-
rupted current in this case also. Again then the action of the internqsted
current upon the contraction force of the ventricular strip is the same as
that of the vagus upon the whole ventricle of the tortoise.

J O7). cit.

INNERVATION OF THE HEART.

109

The resemblance between the action of the vagns nerve and the
weak intenupted current upon the conduction power and the contraction
force of the cardiac muscle is therefore in all cases very striking. Not
only are the effects of the stimulation of the nerve precisely similar to
the action of the interrupted current applied directly to the different
muscular strips, but also atropin produces the same effect in each case.
So close a resemblance must have some very definite meaning ; we must
therefore in the first place decide between the one or the other of the two
following propositions, either

An interrupted current apjDlied to the strip of muscle, which is not
strong enough to produce contractions of itself, causes the same effects
as vagus stimulation because it stimulates the endings of the nerves in
the muscle, or else

The action of the vagus nerve upon the muscular fibres is of the same
nature as that of a weak interrupted current upon those same fibres.

If the first of these two propositions is true, then every experiment
involving the electrical stimulation of the cardiac muscle which has
hitherto been performed must be rediscussed on the assumption that the
effects observed may to some extent be due to the excitation of the
endings of the vagus nerves, for unfortunately in the case of the cardiac
muscle we cannot with certainty separate nervous from muscular action
by means of curare. Such a conclusion however is hardly warranted,
for if the interrupted current when applied directly to the muscle pro-
duces its effects by the stimulation of the endings of the vagus nerves,
then other kinds of stimulation must also produce similar results,
when applied to the muscle as when applied to the vagus itself; single
induction shocks therefore ought to produce the same effect whether
applied to the vagus or the muscle itself. Bowditch’s experiments have
conclusively sho^vn that a series of single induction shocks applied to
the muscle of the frog’s ventricle causes a series of contractions in the
form of an ascending staircase, and the same effect is seen in the mus-
cular strip from the apex of the auricle or ventricle of the tortoise ; on
the other hand, a series of .single induction shocks aiDplied every three
or five seconds to the vagus nerve of the tortoise reduces the force of the
auricular contractions in the most marked manner as long as the induc-
tion shocks are sent through the nerve. Fig. 18, curve ll., PI. V. ; nay more,
a single shock applied to the vagus trunk is sufficient to reduce the next
five or six auricular contractions as is shown in Fig. 18, curve l. In fact no
better stimidus could be rerpiired to set the vagus in action than a series
of single induction shocks every five seconds. So much can then be

9—2

110

IK. II. GASKELL

said, single induction shocks affect the cardiac mu.scle in a manner
directly opposite to their effect when applied to the vagus nerve; for
this reason it is more probable that the second proposition Ls true viz.
The vagus produces the same effects on the contraction
force and conduction power of the cardiac muscle as an
interrupted current applied to the muscle directly, which
is too w^eak to cause muscular contractions.

In order to make the resemblance between the action of the vagus
and the interrupted current complete, it must be shoA\m that the latter
is able to affect the rhythm in a manner similar to the former and that
atropin prevents that effect in the same way in both cases. Up to the
present such evidence is by no means complete, although I cannot help
thinking that a large number of experiments made by former observers
are in reality to be explained by the direct action of the stimulation,
rather than by the supposition that the stimulus excites inhibitory
nerves or inhibitory centres. Again and again it is seen that the direct
stimulation of the place from which the rhythm starts causes a slowing
or absolute cessation of that rh3rthm. Thus Foster and Dew-Smith*
have shown that an interrupted or constant current sent through the
rhythmically contracting heart of the snail, or through the ventricle or
auricle alone when beating automatically, produces a standstill or
slowing during the passage of the current. So too in the Vertebrata, the
direct stimulation of that part of the heart from which the rhythmical
contractions arise, viz, the sinus venosus, is a most certain method of
obtaining standstill of the heart, and here too we have a further remark-
able fact, that atropin prevents that standstill from taking place just as
it prevents the depressing effects of the stimulation of the strip of
cardiac muscle upon the force of the contractions. So too, as Ranvier®
has pointed out and as I have seen again and again in the case of the
tortoise, the direct stimulation of the right place in the isolated auricle
inhibits the automatic rhythm of the auricle. In this case as well as in
the case of the sinus venosus, it is commonly supposed that such a stand-
still indicates the existence of special inhibitory centres which are
excited by the stimulation. I venture however to submit that in these
cases as well as in the snail’s heart such inhibition is the result of the
direct stimulation of the muscular tissue from which the rhythmical
contractions originate, and is therefore strictly corajjarable to the diminu-
tion of contraction force observed in the muscular strips from the apex

J Froc. Roy. Soc. No. 160, 1872.

- Lei^miK d’Antitomie. Genfrale. Paris, 1880, p. 161.

INNERVATION OF THE HEART.

Ill

of the frog’s ventricle and tortoise auricle as already described. Still I
must confess that in the case of the muscular strips when beating auto-
matically with a perfectly regular rhythm (as in Fig. 17, PI. V.), the stimu-
lation which is sufficient to depress most markedly the force of the
contractions may be absolutely without effect upon the rate of the
rhythm. It does not however follow that such a rhythm cannot be
inhibited by the direct application of the interrupted current; it is
possible that a strength of current which is able to depress the contrac-
tions may not be strong enough to influence the rhythm; while a stronger
current sufficient to inhibit the rhythm might at the same time induce
contractions in some part or other of the muscular strip and so hide the
inhibition really produced. Such an explanation is plausible to this
extent ; in all rhythmically contracting portions of the heart any direct
stimulation, which is strong enough to cause a series of contractions
follomng each other with greater rapidity than the previous rate of
rhythm, is very apt to be followed by a pause which is of longer duration
than the previous regular pauses between the consecutive automatic
contractions. Such a pause does not necessarily prove that the rhythm
has been inhibited by the stimulation and I therefore prefer for the
present to leave it doubtful whether the direct stimulation of a rhythmi-
cally contracting tissue can in all cases inhibit the rhythm of that tissue.

PART IV.

On the action of atropin and muscarin.

The observations of Bowditch* upon the effects of atropin and mus-
carin on the force of the contractions of the cardiac muscle are typical
of the action of these drugs upon every function of the cardiac muscle.
His results may be expressed by saying:— Atropin brings the contraction
power of the muscle to a maximum straightway, so that the beneficial
effects of successive stimuli disappear. Muscarin depresses the power of
contraction without removing the effects of successive stimuli, so that
the maximum contraction obtained is much less, though the “staircase ”
still remains. Expanding these two assertions so as to include all the
functions of cardiac muscle we should expect to find that atropin
improves the rhythmical power and the conduction power in the same
way as the contraction force, such an improvement being of a fixed and

* Op. cit.

112

W. II. GAHKKLL.

stable character, though not necessarily lasting. On the otlier hand,
muscarin ought to depress every function without preventing the
possibility of a limited amount of improvement in that function.

All experimental evidence serves to confirm this view. Thus
SokoloS* has shown that the application of atropin re.stores the
rhythmical power when it has been depressed by the application of a
variety of different drugs. And I shall show later on that atropin
quickens the development of an automatic rhythm, and removes the
“staircase” of rhythm in the same way as it removes the “stair-
case” of contraction force. Not only does this drug develope the
rhythmieal power in the same Avay as the contraction force, but it
produces the same sort of stable effect upon both. In the first stage of
its action neither the stimulation of the cardiac nerves nor direct
stimulation of the muscle is able to depress the rhythm or the force of
the contractions ; the augmenting efiect alone remains ; the beats are
simply quickened and increased in force. Later on, this efiect also
disappears ; neither by nervous action nor by dhect stimulation can any
alteration either in rhythm or force of contraction be effected. The
action of atropin then is to bring about a certain maximum of rhythmical
power and contraction force of such a stable character that this maxi-
mum is with the greatest difficulty displaced in either one direction or
the other. It must not however be supposed that the action of atropin
is a purely beneficial one, that it is trophic in the same way as the vagus
and the interrupted current, which produce permanently beneficial
efiects; in the unfed heart outside the body its beneficial effects are
followed, with a rapidity varying according to the extent of the dose, by
a marked depressing action; the force of the contractions steadily
diminish, the rhythm becomes slower and slower. In the frog’s heart,
when removed from the body, this depressing effect on the rhythmical
power is manifested very early, so that, as pointed out in my paper, the
rhythm may be markedly slowed at the same time that the force of the
contractions is as strong or even stronger than before. In precisely the
same way the improvement in conduction power which the atropin at
first causes is followed by a diminution of that power, so that the
ventricle responds to every second contraction only of the auricle or,
what is frequently seen in the atropinized heart, responds to every two
out of three auricular contractions. No doubt these depressing after-
effects are due mainly if not entirely to an overdose of the dnig,
combined 'with the absence of nutrient material.

^ riiysiolofi. und to.vicolog. Sliidicn nm Herzen, Bern, 1881.

INNERVATION OF THE HEART.

113

In my former paper I have throughout spoken of the action of
atropin and muscarin as affecting the strength of the impulses from the
motor ganglia to the ventricle. In all instances where such phraseology
occurs it is clear that in reality the phenomena observed were due to
an alteration of the conduction power during the passage of the con-
traction wave from auricle to ventricle. Muscarin acts upon the cardiac
muscle in such a way as to depress every one of its functions, but its
action is much more labile than that of atropin. For a long time at all
events such depression of function can be affected by nervous and direct
stimulation in both directions ; it can be both increased or diminished
up to a certain limited extent. So too the effect of muscarin can be
counteracted immediately by the more stable action of atropin.

The depressing effect of muscarin upon both the rhythmical and con-
traction power has been so often observed as to admit of no doubt. The
same effect upon the excitability and conduction power of the muscle has
been noticed by me in my former paper, and can be seen in the most ex-
cellent manner by observing its action upon the suspended strip from the
auricle of the tortoise. As already mentioned the exciting electrodes, by
means of which single induction shocks are sent into the strip every five
or ten seconds, are placed at the fixed end of the strip, so that the
current jjassing between their poles passes through a small portion only
of muscular tissue at that fixed end. When therefore a single induction
shock is sent in, that small portion of tissue alone is directly stimulated
and the contraction of the whole strip is due to the spreading of the
contraction wave from this initially stimulated portion. When the
force of the contractions and the conduction power has been sufficiently
improved by the combined action of the single induction shocks and
the weak interrupted current sent through the whole strip as already
described, then each contraction started by the exciting electrodes passes
(piickly along the strip, and no distinction can be drawn between the
contractions of the small piece between those electrodes and the rest
of the strip. After the application of muscarin matters are different ;
not only is the force of the contractions markedly diminished, but a
distinct hesitation is seen before the initial contraction spreads over the
whole strip. This hesitation may become greater and greater until a
partial block is caused of such a character, that every second induction
shock causes a contraction which is confined to the piece of muscle
between the exciting electrodes, while the rest of the stimuli cause a
contraction which travels through the whole strip. Under such circum-
stances the passage of the weak interrupted current still further reduces

in-

W. II. GASKJIJ.L.

tllG toiCG oi tllG COlltl cXCllOnSj Hilicl Illtiy CflUS© SUcll £1 Ijlockiii^ of £t
larger number of contractions, or may diminisli the excitability to such
an extent that not even the i^ortion between the exciting electrodes
contracts when the single induction shock is sent through. If now a
drop of a weak atropin solution be applied to the strip, the contractions
instantly increase in force in a wonderful manner, every contraction
passes easily and quickly from end to end, all sign of an initial con-
traction of the muscle between the exciting electrodes immediately
vanishes, and in a very short time the interrupted current is able to do
nothing more than slightly to diminish the force of the contractions
during its passage.

Both atropin and muscarin produce the effects above mentioned by
directly modifying the various functions of the cardiac muscle, and in
proportion to the stability of the effect so produced is the possibility of
a modification of that effect by the direct stimulation of the muscle or
by the action of the cardiac nerves. It is partly because the atropin
acts on the muscular tissues in such a way as to keep the various mus-
cular powers fixed in a relatively high state of activity, that the cardiac
nerves are unable any longer to depress those powers. It is because
atropin is able to restore the rhythmical power of the muscle, that
stimulation of the vagus and of the sinus is no longer able to produce
inhibition ; it is because the atropinized muscle contracts with the very
first stimulus at its full strength that neither the cardiac nerves nor the
interrupted current is any longer able to diminish those contractions ;
it is because atropin repairs the conduction power that stimulation of
the vagus is no longer able to prevent the contraction wave passing
from the sinus into the auricles.

Atropin, however, has a further action which is not possessed by
muscarin. It not only prevents the action of the vagus nerves by
its direct influence on the cardiac muscle, but also by its action on
the intra-cardiac nerves themselves, and perhaps especially on their
ganglionic nerve cells. Muscarin, on the other hand, influences the
muscular tissues, leaving the nervous action intact, at all events, until
a very large dose has been given. Thus in my former paper I noticed
in the case of the frog that atropin, applied to the sinus and auricle
alone, prevented the whole action of the vagus not only on those parts of
the heart, but on the ventricle as well ; while, on the other hand, mus-
carin when applied to the sinus and auricle only may affect those parts
even to complete standstill, without in the least abolishing the power of
(ho vagus to increase the contractions of the ventricle.

INNERVATION OF THE HEART.

115

In the tortoise the influence of atropin upon the action of the vagus
can be demonstrated by the effect upon both the force of the auricular
contractions and the conduction power of the auricular muscle, wheir the
atropin is applied locally to the point of entrance of the coronary nerve
into the auriculo-ventricular groove. Thus in one case, where the auricle
was slit up until only every second contraction passed the block, it was
found that stimulation of the right vagus and of the coronary nerve was
in each instance able to remove that block, and also, as is always the case,
stimulation of each nerve diminished the contractions of the part of the
auricle on its own side. Atropin (1 p. c. solution) was then applied to the
ventricle and its junction with the ventricle-auricle, with the result of pre-
venting the action of the coronary nerve upon the force of the contractions
of the ventricle-auricle and upon the conduction of the contraction wave
over the block (as is seen in Fig. 19, PI. V.). On the other hand, the right
vagus was still able to slow the rhythm, reduce the force of the contrac-
tions of the sinus-auricle and remove the block of the contraction wave,
just as efficiently as before atropin had been given (Fig. 19). Similarly
atropin applied to the sinus and sino-auricular junction will remove the
whole action of both right and left vagus nerves, without affecting the
action of the coronary nerve, provided that the auricle has been
previously slit up, and so all chance of the drug reaching the auri-
culo-ventricular junction removed. Atropin then not only influences the
muscular tissue, but also the nervous structures of the heart in such a
way that neither the direct action of the interrupted current nor stimu-
lation of the vagus nerves are any longer able to produce their usual
effects upon the various functions of the cardiac muscles.

The views put forward in this paper necessitate a revision of the
opinions at present held in respect to the action of a large number of
cardiac poisons : a task, which it is impossible to undertake in this
present paper without swelling it out to an inordinate length. I will
therefore confine myself to one or two remarks on the action of curare
as illustrative of the position I desire to maintain.

The difference between the action of curare and atropin is one of
the main arguments in favour of the existence of an inhibitory centre
capable of being paralysed by atropin but not by curare. Both poisons
prevent the inhibitory action of tbe vagus nerve ; but while after curare
inhibition can still be caused by the direct stimulation of the venous
sknis ; after atropin this is no longer possible. The inhibition caused by
muscarin can be removed by atropin, but not by curare. These facts do
not in my opinion in the slightest degree prove the existence of an

IIG

W. II. GAHKELL.

inhibitory centre ; they simply confirm tlie well-known fact that curare
is essentially a poison which affects nervous and not muscular structures,
and give another proof of the affinity of the cardiac muscle and nerve to
the ordinary striated muscle and nerve. Thus curare prevents the inhibi-
tory action of the vagus, because it paralyses some part or other of the
nerve endings. It does not prevent the inhibition caused by the direct
stimulation of the venous sinus, because unlike atropin it does not act
upon the muscular tissue of the sinus, and therefore cannot prevent the
inhibitory action of the current applied directly to that muscle. For
the same reason it is unable to influence the inhibitory action of a
muscular poison like muscarin.

PART V.

Conclusion.

The conception of the cardiac function advanced in the preceding
pages represents the heart as a specially modified portion of the. vascular
system ; the heart is to be considered as a piece of arter}’- or vein, the
muscular walls of which have developed in a special manner. The key-
note therefore of the peculiarities of the cardiac muscle consists in its
stnictural position, intermediate between unstriped and striated muscle
fibre. Muscular tissues exhibit three different modes of responding to
stimulation according to their structure. These modes may be expressed
by saying that certain muscles possess essentially the power of “tonic
contraction,” others the power of “rhythmical contraction,” and others
that of “rapid contraction.” A comparison of the tetanizing action of a
strong interrupted current upon a strip of muscle from the bladder of
the tortoise and from the heart of the tortoise with the ordinary tetanus
curve of the frog’s gastrocnemius shows clearly the difference of the
three kinds of muscular tissue.

The unstriped muscle of the bladder contracts slowly after a long
latent period, the contraction increasing steadily in force during and
even after the cessation of the tetanizing current, and then the strip
returns with excessive slowness to its original length. In other words
we see a prolonged tonic contraction as the result of the stimulation.

With the striated muscle we have the well-known curve of tetanus
composed of the superposition of a series of rapid contractions.

The cardiac strip gives a curve Avhich is intermediate between the
two and may be described as consisting of a long-continued tonic con-

INNFAIVATION OF THE HEART.

117

traction upon which a number of rapid contractions are super-imposed.
These separate rapid contractions never succeed one another so quickly
as to fuse together. The cardiac muscle then, when tetanized, gives in
virtue of its relationship to unstriped muscle, a tetanus of tonicity (to
use Ranvier’s expression), and at the same time a series of rapid con-
tractions in consequence of its affinity to ordinary striated muscle.
When the vitality of the tissue is impaired by exhaustion, by injury, by
malnutrition, the cardiac muscle loses its power of rapid contraction, and
the less- specialized tonic power alone remains, the muscle strip tetanized
when in that condition contracts with a prolonged tonic contraction in
the same way as unstriped muscle.

In another respect too the intermediate position of the cardiac
muscle between the slowly contracting, slowly exhausted unstriped
muscle and the rapidly contracting easily exhausted striated musele is
clearly shown; the vitality of unstriped musele after the death of an
animal is wonderfully long ; the irritability of the cardiac muscle after
death is less than this, but decidedly greater than that of the ordinary
striated muscles.

Again, the evidence that the power of rhythmical contraction is
a property of muscular tissue, common to many of the different kinds
of muscle found in the animal kingdom increases in importance day by
day. Not only do we know that the unstriped muscle of the ureter and
the veins of the bat’s wing are as capable of contracting rhythmically as
the apex of the frog’s heart under the influence of the mechanical
stimulus of distention, but we also have evidence that the more highly
developed striated muscle fibres are capable of rhythmical contractions
under the influence of a constant stimulation, whether electrical or
chemical. This is especially the case, as the experiments of Schoenlein’
prove, in the striated muscles of the invertebrata, which contract rhyth-
mically upon stimulation by a weak interrupted current in a manner
very similar to the muscular tissue of the apex of the frog’s heart. We
see then that the power of rhythmical contraction is not confined to
cardiac muscle, but exists also to a certain extent in unstriped and
striated muscles, and just as this power has been developed to a greater
extent in some unstriated muscles than in others, so too it has reached
a still higher stage — the stage of rhythmical automatism — in some kinds
of cardiac muscle than in others. We may then make a comparison
between the development of function in the three kinds of muscular
tissue as follows : —

' Archivf. Fliijsiolo<jic von clii Bois-lleymond, 1882, p. 369.

118

W. H. GASKELL.

Striated muscle of vertebrates —

Ea^jidity of contraction most highly developed.

Tonicity rudimentaiy.

Rhythmic action still more rudimentary.

Cardiac muscle —

Rhythmic action most highly developed.

Rapidity of contraction well marked.

Tonicity well marked.

Unstriped muscle —

Tonicity most highly developed.

Rhythmic action well marked.

Rapidity of contraction most rudimentary.

Further, the development of the full rhythmical power in a piece of
cardiac muscle is strikingly similar to that of the full contraction power.
Thus the rate^of the automatic rhythm increases by successive incre-
ments in the same way as the contraction force, and just as the isolated
muscle inBowditch’s experiment responds weakly to the 6rst stimula-
tion, so the isolated auricle or ventricle of the tortoise remains still for
some time before the first automatic contraction takes place.

The meaning of this preliminary standstill — the standstill of the first
Stannius ligature — has always been a difficult problem to solve, and
many attempts at an explanation have been given. It is therefore o^
special interest to examine the conditions necessary for its appearance
and for its non-appearance. It is clear from what has already been said
that this standstill is of the same nature, whether it occurs as a pre-
liminary to the automatic rhythm of the auricle, of the ventricle, or of
the apex of auricle or ventricle. It is associated with the development
of the automatic rhythm in each case, and is not due to the action of
any special inhibitory mechanism. The laws of the development of
rhythm are throughout very similar to the laws of the development of
the contraction force, and the reason why the tissue when first isolated
commences its automatic contractions at so slow a rate as to give
occasion to the use of the term “standstill” is the same as the reason
why the first artificial contraction of the muscular tissue of the apex in
Bow ditch’s experiment is so much weaker than the subsequent contrac-
tions. If it were possible to ensure that the conditions of the experi-
ment should be the same in every case, it would in all probability be
found that the length of the standstill after isolation of the tissue was
strictly in proportion to the rhythmical power of the tissue. We ought
therefore to find that the auricle commences its automatic beats sooner

INNERVATION OF THE HEART.

119

after isolation than the ventricle, and the ventricle sooner than the strip
from the apex. Undoubtedly the standstill is longer in the case of the
apex than of the whole ventricle, and sometimes it is very clear that
the isolation of the ventricle is followed by a longer standstill than that
of the auricle, as the following case shows.

Feb. 14, 1883. Heart suspended, aorta held. Auricle fixed to upper
lever, ventricle to lower. Contractions perfectly regular at about 12 per
minute. The sinus was then cut away ; 5 excitation contractions occurred
at the moment of section and then the auricle and ventricle remained still
for 11 minutes, after wliich the first automatic contraction of the auricle took
place, followed by a contraction of the ventricle. The auriculo-ventricular
rhythm then developed in its usual manner, the lengths of time in seconds
between consecutive beats being as follows —

260, 170, ?, 90, 80.

A fresh drum was here necessary, and as soon as the beats were again
recorded the durations in seconds of consecutive pauses were

33, 33, 27, 27, 28, 24, 23 5, 23, 22'5, 22, 21-5, 22, 21, 20, 19-75, 19-5, 19,
19, 19, 18-5, 18, 18.
and again on the next curve

16-5, 16.

The auricle was now cut away and a rhythm of excitation was immedi-
ately set up in the ventricle with pauses between the beats as follows —

7, 8, 9, 10, 10, 22, 22, 20, 23, 25, 26, 28, 35, 40, 106, 100, ?, 193, 170,
154, 1,

and then complete standstill for 12 minutes.

After this the ventricle began to beat automatically with the following
lengths of time between the contractions —

150, 145, 138, 134, 130.

The first standstill lasted therefore 11 minutes and the second standstill
including the time of the rhythm of excitation at least 34 minutes.

Throughout, the length of the standstill is relative and not absolute,
so that it is not jiossible to compare different experiments on different
animals without making an extensive series of experiments with all
possible precautions in order to solve this one particular point. This I
have not yet done and cannot therefore assert positively that the length
of the standstill varies inversely as the rhythmical power of the heart seg-
ment which is isolated, although such a i^roposition is highly probable.

The nature of this standstill is further shown by the conditions
necessary for its non-appearance. These conditions may be summed up
in the a.ssertion : Any influence which increases the develoj^-

120

ir. II. GASKELL

ment of the rhythmical jDower removes at the same time
the preliminary standstill; just as in BoAvditch’s experiment,
atropin brings the force of the contractions to an immediate maximum.
Such influences are in the case of the ventricular standstill the supply of
a blood solution through the coronary vessels and the application of
atropin to the auriculo-ventricular groove. In both cases the ventricle
beats immediately upon isolation, the standstill is gone.

Again, when the contractions of the frog’s ventricle have reached
their maximum by means of a series of single induction shocks at equal
intervals, and then the stimulations are discontinued for some time, a
new set of contractions caused by a second series of induction shocks
does not begin Avith contractions of the maximum strength of the
IDrevious series, but the first of the new set is smaller than the last of
the old and a staircase is again formed. So too an automatic rhythm
which has developed up to a certain rate may recommence at a sloAver
rate after it has been interrupted. This is exemplified in the folloAving
Avay. The auricle is slit until a block occurs ; in many cases this block
lasts so long as to alloAV time for the commencement of the development
of a rhythm of the ventricle and that part of the auricle in connection
Avith it, which is entirely independent of the rhythm of the sinus. At
this time then the two parts of the heart Avhich are separated by the
blocking point are beating quite independently of each other and the
rhythm of the ventricular side is gradually gaining in rapidity in the
usual manner. The block is noAV removed by the application of salt
solution and stimulation of the vagus, until at last in favourable cases
every contraction again passes and the sequence is fully restored. With
the restoration of the sequence the indejjendent rhythm disapjAears, the
ventricle and ventricle-auricle are again completely under the domination
of the sinus. The sinus is noAV removed by the section of the sinus-
auricle, without therefore injuring in any AAny the ventricle and
venti'icle-auricle ; and it is found that a standstill again occurs and again
the independent auriculo-ventricular rhythm is sloAvly deA'^eloped iqi to
and beyond its former rate. Although the second rhythm does not
commence at the rate that had previously been reached, yet some bene-
ficial effect of the previous development is usually noticed; the second
stand.still is not as long as the first, and a third standstill produced in a
similar manner may be less still, until at last the production of a block is
not folloAved by any stand.still at all.

The similarity betAV'een the laAvs governing the rhjdhmical poAA’er
and the contraction force of the cardiac mn.scle is not the only similarity

INNERVATION OF THE HEART.

121

found between two different muscular attributes. The excitability of
the muscle as measured by its capability of response to a stimulus, and
its power of conducting a contraction from muscle cell to muscle cell
present many resemblances to each other. It has been shown that a
block can be produced, either by artificial section of the auricle or by
an increase in the natural block at the auriculo-ventricular junction,
such that only every second contraction which starts from the sinus passes
over the block. Such a partial block has been shown to be dependent
upon the rate of the contractions and not upon the strength of the
stimulus which initiates the contraction wave. Thus the conduction
power of the muscle at the blocking point may be such that every
contraction at ten seconds intervals will pass, while only every second
contraction at intervals of five seconds is able to pass. In precisely the
same way w'e know that the cardiac muscle will respond to every
stimulus when a sufficient length of time elapses between the stimuli,
but only to every second stimulus when that time is too short, provided
that the strength of the stimulus remains unaltered. Again, in conse-
quence of stimulation of the vagus, every contraction may pass a block
over which only every second contraction had previously been able to
pass, even though at the same time the force of the contractions has
been greatly diminished. The conduction power is not dependent upon
contraction force. So too the excitability of the muscle may be increased
by the same action which depresses the force of the contractions. Thus
as already mentioned the strip of muscle from the apex of the frog’s
ventricle or tortoise auricle may respond to every second induction shock,
when the induction shocks are sufficiently weak and are sent through every
five seconds ; yet upon sending through a weak interrupted current, the
muscle may respond to every stimulation, though at the same time the
force of the contractions is markedly diminished. I have not yet
attempted to work out the relations which exist between the strength
of the interrupted current, the alteration of the contraction force and
the alteration of excitability, and can say therefore at present nothing
more definite than that the excitability of the muscle may be influenced
by the interrupted current in a direction opposite to the contraction force.
In other words, the interrupted current affects the muscular excitability in
a manner similar to the effect of the vagus upon the conduction jjower ;
another proof of the resemblance between the action of the vagus and a
weak interrupted current and also of the close relationship between
mu.scular excitability and conduction power.

Again, I have shown clearly that the vagus depresses and exalts

122

W. II. GAHKELL.

all the different functions of all the different muscular tissues of the
heart, whether the function in question is rhythm, contraction, con-
duction, tone, or excitability. Also I have shown that depression
of one function is not necessarily accompanied by a simultaneous
depression of another function, and so also with the exaltatioh of
function. Further, the exaltation of each function is not nece.ssarily
dependent uj^on a iDrevious depression ; in each case the primary effect
may under certam circumstances be exaltation and not depression.
Combining these two facts together we are driven to accept one of
two alternatives, either the vagus contains a multiplicity of fibres,
which can be divided into two groups after the fashion of Heidenhainb —
1. Depressors (Hemmungs-fasem); 2. Augmentors(Verstarkungs-fa.sem);
and further each member of each of these groups has again its own
special function, so that for instance the rhythm-inhibiting nerve fibre
is different in kind from the contraction-depressing fibre and so on ;
or else, the same trophic nerve fibre produces all the different effects
observed, according to the nature of the muscle which it suppbes, and
the condition of that muscle at the time. ^

In this paper as well as in my previous jDaper all the facts have
tended strongly to prove that the vagus acts in the same manner upon
the rhythm of the heart and upon the force of its contractions, so that if
separate inhibitory and accelerator nerve fibres exist for the one, separate
depressor and augmentor fibres nmst exist for the other. If therefore it
can be shown that such diminution and augmentation of the strength of
the contractions are due not to different influences reaching the muscle,
but to the same influence affecting the muscle when its conditions are
different, then it is, to say the least, highly probable that slowing and ac-
celeration are also due not to different nerve fibres but to the action of the
same nerve fibre under different circumstances. In the frog, as I have pre-
viously pointed out, such a complete gradation exists between a primarj'
excessive diminution of the contractions and a primary augmentation
in consequence of nerve stimulation, as to render the hypothesis that
such curves depend upon the simultaneous stimulation of two antago-
nistic nerve fibres very improbable. I have now proved in addition that
a weak interrujited current applied to the smallest strip of cardiac
muscle produces the same two opposite effects, and that here the depres-
sing effect maybe removed and the augmenting alone remain, when the
condition of the muscle is altered by the application of atropin. In

* Op. rit.

IXNERVATION OF THE HEART.

123

order therefore to still hold to the view of specific nerve fibres acting in
opposite directions upon the force of the contractions, it is necessary to
assume, not only that those nerve fibres j^ossess opposite qualities up to
their very termination in the muscle, but that even when the muscle
itself is stimulated the relative action of these two sets of nerves still
holds its ground. In addition, atropin would have to be considered as
acting upon these two sets of nerve endings and not upon the muscle,
paralysing the depressor nerve endings before those of the augmentor
nerves. The experiments of Luc h singer and Szpilman‘ which lead
them to the conclusion that atropin has a special action upon unstriped
muscle fibre, those of Bo wd itch already referred to, and my own all point
to the conclusion that atropin affects the cardiac muscle directly, in conse-
quence of its affinity to unstriped muscle fibre. The whole evidence goes
to show that the vagus is a constructive and not a destructive nerve, that
the initial depression of function is not of the nature of exhaustion but
is preliminary to a greater functional activity. The phenomenon presented
by the muscular tissue of the frog and tortoise under the influence of an
induced current is of exactly the same nature as that seen in the muscle
of the snail’s heart (as pointed out by Foster^ and Dew-Smith), when
a constant or weak interrupted current is sent through it. In both cases
augmentation of function occurs as well as depression ; in the one case
the evidence is as strong in favour of special inhibitory and accelerator
nerves as in the other. Clearly in the case of the snail it is simply
impossible, as Foster® has said, to explain such results by the presence of
accelerator and inhibitory fibres in every strip of muscular tissue, when
as a matter of fact, cardiac nerves of any kind whatever have not been
proved to exist. Clearly also whatever explanation will ultimately be
found for the action of the current upon the muscular tissue of the
snail s heart will also explain the same phenomena in the heart of the
frog and tortoise. The problem which demands solution is essentially.
Why is the condition of the muscle, ultimately improved in every one of
its functions by the direct application to it of a continuous stimulus
which is not strong enough to produce motor effects ? and why is that
improvement of function preceded in many cases by a diminution of
function? When these two questions have received a satisfactory
answer, it will no longer be strange that the vagus produces throughout
two opposing effects, and the action of atropin will become clear ; then
the relationship between trophic and motor action will be understood,

’ P Auger’s Archiv, Vol. xxvi. p. 4,59. a Op. cit.

^ Journ. Avat. avA Phy«iol. VoL x. “Some effects of Upas Antiar ou the frog’s heart.”

124

W. 11. OAHKKLL

and the true function of the ganglion cells found in connection with
nerve fibres will be indicated. At present it can only be said that the
vagus is the trophic nerve of the cardiac muscle, its action resembling
that of a stimulus too weak to produce motor effects, and therefore it is
possible that the function of the ganglion cells in the course of the ner\’e
is to convert an otherwise motor into a trophic nerve.

Throughout this paper I have confined myself to observations upon
the heart of cold-blooded animals. I am not yet in position to say how'
far, in the more highly-developed mammalia, the phenomena of the
heart may have become changed under a greater differentiation of
function, and an increased complexity of structure. Such questions
therefore as the real interpretation of the action of the accelerans nerves,
as distinguished from that of the main vagus fibres in these animals,
must be left for subsequent investigation. I trust to be able at some
luture time to deal with the matter, which has naturally already been
the object of investigation by others.

DESCRIPTION OF FIOURES. PI. II.— V.

All curves read from left to right. The fractions in brackets after certain
of the figures denote the extent to which the original curve has been reduced
by photography. The letters S, A, F in all cases denote beats of the sinus,
auricle and ventricle respectively.

Fig. 1. Feb. 23, 1882. DevelojDment of the rhythm of the auricle.

Curve A. Sinus cut away at arrow. The first curve after section
is marked i. ; ii. is the continuation of this curve on the same drum.

Curve B. Continuation of curve A. Drum changed as rapidly as
possible.

Curve C. Continuatio]-! of curve B. Fresh drmn. Time marker
every 2 seconds.

Fig. 2. Feb. 9, 1882. Development of the rhythm of the whole ventricle.

Clamp tightened in auriculo-ventricular gi’oove. A rhythm of ex-
citation was set up in the ventricle which gradually slowed down to
the minimum I'ate shown at the commencement of curve i. From
this point the ventricular rhythm slowly and regularly quickened as
shown in curves i. — vii. Time marker every 2 seconds.

Ciu’ve I. was taken at 12.15 p.m.

Curves II. and iii. follow immediately on curve i. and were therefore
taken at about 12.30 and 12.45 p.m. respectively.

!

INNERVATION OF THE HEART. 12")

Curve IV. was taken at 2.45 p.iu.

„ V. „ „ „ 4.0 p.m.

„ VI. „ „ „ 5.15 p.m.

„ VII. „ „ „ 6.40 p.m.

Fig. 3. Nov. 7, 1882. Development of the rhythm of the ventricular strip.

Strip from apex of ventricle suspended at 3.30 p.m.

Single induction shocks every 10 seconds sent in at one end ;
interrupted current sent through the whole strip at intervals as
marked on the upper stimulation marking Ime.

Curves i., ii., iii. are samples taken during the first hour after
suspension ; each contraction corresponding to a single induction shock.
Time marker every 10 seconds.

Curves iv., v. are samples of the automatic beats taken between
5.30 and 6 p.m. Time marker every 2 seconds.

Cmwe VI. was taken at 11 a.m. on Nov. 8; the strip remaining
undistui'bed during the night. Time marker every 2 seconds.

Fig. 4. Feb. 27, 1882. Comparison of artificial with natural block.

Aorta held ; auricle slit up.

j Curve A. Each auricular beat is composed of three parts,

i First the contraction of the sinus-auricle (As) ; then the contraction

j of the ventricle-auricle (Av) ; and then the ventricular contraction ( V)

i which follows Av and is transmitted to the ujiper lever.

■ Curve j8. Between curves A and £ the auricle was slit up further;

the pause between the contractions of As and Av was increased, and
every second contraction of As was unable to pass the block and there-
fore no contraction of Av or V followed. Time marker every 2
seconds.

Fig. 5. May 8, 1882. Stimulation of L. Vagus, R. Vagus and Coronary
Nerve.

Aorta held. Time marker every 10 seconds. Sec. coil at 10 c.m.

Fig. 6. May 20, 1882. Stimulation of Coronary Nerve (central end).

Auricle cut away from ventricle, leaving coronary nerve in connec-
tion both with ventricle and sinus. Aorta held; electrodes on coronaiy
nerve near ventricle. • Contractions of auricle only given, ventricle
quiescent. During both stimulations given in curve, sec. coil at 10
and 12 c.m. respectively, the ventricle remained absolutely quiescent.
Time marker every 2 seconds.

Fig. I. Feb. 27, 1882. Stimulation of R. Vagus when the coronary nerve
is the only channel of communication.

Aorta held. Auricles cut away from sinus, leaving coronary nerv6
intact. Stimulation of R. Vagus in the node after the establishnumt

10—2

12G

W. II. GASKELL

of a regular independent auriculo-ventricular rliythm. Sec. coil at
5 c.m. Time marker every 2 seconds.

Fig. 8. Feb. 13,1882. Development of an independent ventriculo-auricular
rhythm made manifest by vagus stimulation.

Clamp in auriculo-ventricular gi’oove. Curves i. — v. are samples
taken at intervals of the effects of stimulation of the E. Vagus; sec. coil
at 12 and 10 c.m. The arrows V.A and A.V denote the beginning
and the end of the unmasked ventriculo-auricular rhythm during each
stimulation. In this case the after-acceleration is weU marked. Time
marker every 2 seconds.

Fig. 9. March 23, 1882. Stimulation of E. Vagus.

Heart in the body and cii’culation intact. Beats of ventricle only
registered. Sec. coil at 6 c.m. Time marker every 2 seconds.

Fig. 10. Hov. 6, 1882. Eemoval of a partial block by stimulation of E.
Vagus.

Aorta held. Auricle slit up until only every second contraction
j'assed the blocking point. Stimulation of E. Vagus caused aU the
contractions to pass for a time. ^

Fig. 11. March 1, 1882. Eemoval of a partial block by stimulation of E,
V agus.

Aorta held. Auricle slit up until only every second contraction of
As passed. Stimulation of E. Vagus; sec. coil at 8 c.m. After the
second stimulation given in the Fig. the contractions all passed perma-
nently, so that a new block had to be made in order to repeat the ex-
periment. Time marker every 2 seconds.

Fig. 12. May 8, 1882. Increase of partial block by stimulation of the
Coronary nerve.

Aorta held. Auricle sbt up. Stimulation of coronary nerve.
Sec. coil at 8 c.m. Time marker every 10 seconds.

Fig. 13. April 27, 1882. Increase of a partial block by stimulation of the
E. Vagus nerve.

Aorta held. Auricle slit up. Sec. coil at 6 c.m. Time marker
every 2 seconds.

Fig. 14. Oct. 10, 1882. Sinus beats continue during E. Vagus stimulation.

Aorta held. E. Vagus stimulated; sec. coil at 10 and 11 c.m.
respectively. Ehythm of sinus remains unaltered during the stimula-
tions. With the stronger stimulation the beats of the sinus were
diminished in strength to a greater extent than with the weaker
stimulation. Time marker eveiy 2 seconds.

Fig. 15. Oct. 28, 1882. Lengthening of the pause between the beats of the
sinus and auricle during stimulation of the E. Vagus.

INNERVATION OF THE HEART.

127

Sinus beats [S) are made evident by the stimulation of the nerve.
Sec. coil at 10 c.m.

Fig. 16. Snake’s auricle. Shortening of the pause between the beats of the
sinus and auricle during stimulation of the E-. Vagus.

In the two curves given the stimulation of the nerve commences at
the arrow (a) and ends at the arrow ((d). Sec. coil at 6 c.m. Drum
moving rapidly.

Fig. 17. Nov. 21, 1882. Action of a weak interrupted current upon the
spontaneous contractions of a strip from the apex of the auricle.

By the application of single induction shocks every 5 seconds com-
bined with the interrupted current at intervals the strip had been
brought into the condition of spontaneous beating.

Curve I. gives two examples of the effect of an interrupted current
sent through the strip upon the strength of these spontaneous contrac-
tions. Sec. coil at 9.5 and 8.5 c.m. respectively.

The strip was kept moist through the night and at 12.30 p.m.
on Nov. 22 curve ii. was taken and shortly afterwards curve iii.
Sec. cod pushed gradually from 8 — 5 c.m. and from 8—6 c.m.
respectively. In both curves the contractions of the strip are spon-
taneous. Time marker every 5 seconds.

Fig. 18. Nov. 15, 1882. Action of single induction shocks applied to the
R. Vagus.

Aorta held ; auricular beats only registered.

Curve I. shows the effect of a single strong (sec. cod at 0 c.m.)
induction shock applied to the R. Vagus in the neck.

Curve II. gives the effect of a series of single induction shocks to
the R. Vagus every 3 seconds. Time marker every 3 seconds. Sec.
coil at 0 c.m.

Fig. 19. May 8, 1882. Action of atrojiin applied to junction of auricle and
ventricle.

Aorta held. Auricle slit up so as to cause partial block. Atropin
sulphate (1 per cent.) applied to junction of auricle and ventricle.
Stimulation of coronary nerve (sec. coil at 6 c.m.) is no longer able to
influence either the force of the contractions of Av or the passage of
the contraction from As to Av.

Stimulation of R. Vagus (sec. coil at 6 c.m.) acts as before the
application of the atropin. Time marker every 10 seconds.

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