EXPERIMENTS ON THE RELATION OF THE INHIBI- 
TORY TO THE ACCELERATOR NERVES 
OF THE HEART 
BY 
REID HUNT, Ph. D., M. D. 
(From the Physiological Laboratory of the Johns Hopkins University) 
From 
THE JOURNAL OF EXPERIMENTAL MEDICINE 
VOL. II, No. 2, 1897 EXPERIMENTS ON THE RELATION OF THE 
INHIBITORY TO THE ACCELERATOR 
NERVES OF THE HEART. 
By EEID HUNT, Ph. D., M. D. 
(From the Physiological Laboratory of the Johns Hopkins University.) 
Part I. 
INTRODUCTION. 
The conclusions reached by Baxt* from his experiments upon the 
relation of the vagus to the accelerator nerves of the heart, pub- 
lished about twenty years ago, seem to have been very generally 
accepted. He states in this work that when the two nerves are stimu- 
lated simultaneously, the result during the stimulation is the same as 
when the vagus alone is stimulated, and that this is true even when 
the vagus is stimulated with a minimal and the accelerators with a 
maximal stimulus. 
A few experiments have been published which indicate that this 
view of Baxt is not tenable. Thus Bowditch,f whose work preceded 
and suggested that of Baxt, stated that in his experiments in which 
the two nerves were stimulated simultaneously the accelerator over- 
came the inhibitory nerves as frequently as the latter did the former, 
and very similar results had been obtained by Schmiedeberg still 
earlier; Bayliss and Starling § showed that when the auricles had 
been slowed or brought to a standstill by stimulation of the vagus, 
the ventricles could be made to beat more rapidly by stimulating the 
accelerators; and Meltzer,|| after a careful examination of Baxt’s 
tables, expresses the opinion that the conclusion just the opposite to 
that reached by Baxt is to be drawn from them, viz., that when the 
* Baxt, Arbeiten aus der physiolog. Anstalt zu Leipzig, 1875, p. 179. 
f Bowditch, Arbeiten aus der physiolog. Anstalt zu Leipzig, 1873, p. 259. 
$ Schmiedebeyg, ibid., 1871, p. 34. 
§ Bayliss and Starling, Journal of Physiology, xiii, p. 414, 1892. 
]| Meltzer, Arch. f. Anat. u. Physiol., physiol. Abth., 1892, p. 376. 152 
Relation of Inhibitory to Accelerator Nerves of Heart 
nerves are stimulated simultaneously the effect of the accelerators is 
seen during as well as after the stimulation. Meltzer also calls atten- 
tion to the fact that a stimulation of the vagus arising in the centre 
in the medulla can be overcome by the accelerators, since stimulation 
of these causes an acceleration when the vagi are intact and in tonic 
activity.* 
An examination of Baxt’s tables, moreover, shows that in many 
cases at least the stimuli which he employed for the two nerves were 
not at all comparable with each other as regards their strength, if we 
take their effect upon the heart as the measure, which is evidently 
the only practicable method. Thus his first table shows that the 
stimulus applied to the vagus, instead of being a minimal one, was 
sufficiently strong to cause a slowing of the heart of from forty-four 
to ninety-one per cent; in most cases the figures were nearer the 
latter than the former number. On the other hand, the stimulus 
applied to the accelerators in this series caused in one case an accele- 
ration of thirty-nine per cent; as a rule the acceleration was much less. 
When the stimuli used for the two nerves differed so widely in their 
relative strengths we should naturally expect the inhibitory effect to 
predominate, and the results certainly cannot be regarded as showing 
that a “ minimal stimulation of the vagus can overcome a maximal 
stimulation of the accelerators.” 
Still the conception of Baxt that these nerves are not real antag- 
onists, but that a stimulation of the vagus, whatever its strength, will 
overcome the accelerators even when these are stimulated to a maxi- 
mum, seems to be the prevailing one,f and has served as the basis 
for speculations as to the manner in which these nerves affect the 
heart.:}: 
* Since the completion of this paper Dr. Hough has told me of some experi- 
ments bearing upon this subject which he performed some time ago, but 
the results of which he has not published; he produced standstill of the 
heart by stimulating the vagus, and during the “ escape ” of the heart from 
this standstill (the stimulation of the vagus being continued) the accelera- 
tors were stimulated and a marked acceleration resulted. 
•}■ See, for example, Stewart, Journal of Physiology, xiii, p. 114, 1892, and 
Engelmann, Pfliiger's Archiv, lxv, p. 163, 1896. , 
J Tigerstedt, Lehrbuch der Physiologie des Kreislaufes, p. 271. Leipzig, 
1893. Reid Hunt 
153 
I am convinced from the experiments described in this paper that 
such a view is not tenable; that as far as the ventricle is concerned 
(and this was the only part of the heart investigated in these, as was 
also the case in Baxt’s experiments) these nerves do act as pure 
antagonists to all stimuli which can be fairly compared with each 
other as regards their strength, and the reason that their true relation 
is often concealed is readily accounted for by supposing the inhibi- 
tory apparatus to be more irritable than the accelerator, just as Ruth- 
erford showed that the laryngeal muscles respond to a weaker stimu- 
lus of the vagus than does the heart. 
Before describing the experiments it may be added, in order that 
the problem under discussion may be kept clearly in view, that they 
relate almost exclusively to the effects of stimulating the nerves for 
short periods of time only, i. e., for periods too short for the results 
to be complicated by the fatigue of the accelerator mechanism. This 
was the case in Baxt’s experiments also; but in these the duration of 
the stimulation was often so brief that, as Meltzer points out, we can- 
not be sure that sufficient time was allowed for the full development 
of the effect of the accelerators, which are known to have a very 
variable and often quite long latent period. The effect of stimulating 
the two nerves together for a very long period is, to a large extent, a 
different problem from that discussed in this paper; a few experiments 
bearing upon it, however, will be described in the latter part. 
The results of the experiments will be described under three heads: 
(1) the effect of stimulating the vagus alone, (2) the effect of stimulat- 
ing the accelerators alone, and (3) the effect of stimulating the two 
nerves simultaneously. Under the first tAvo heads some points relat- 
ing to the physiology of these nerves which have been observed 
incidentally will be described. 
The general method of experimenting Avas the same in all cases. 
The animals employed were dogs, cat and rabbits, which were always 
thoroughly anaesthetized in some manner. The heart rate and blood 
pressure were recorded by a mercury manometer in the usual manner. 
The currents to the induction coils used for stimulating the nerves 
were supplied by large storage cells, so that there was little danger of  Relation of Inhibitory to Accelerator Nerves of Heart 
154 
the current becoming perceptibly weaker during the course of an 
experiment. Other details as to the technique will be given in the 
proper place. 
Part II. 
STIMULATION OF THE VAGUS. 
Method. —When the effect of stimulating the vagus alone is to be 
compared with that produced when the accelerators are stimulated at 
the same time, it is obviously necessary to use some form of stimula- 
tion which will give uniform and constant results. This requirement 
is difficult to meet in the case of the vagus, especially as we must 
often deal with minimal or almost minimal stimuli. Both Bowditch 
and Baxt call attention to the inconstancy of the results obtained by 
stimulating the vagus with the ordinary induced current. It seemed 
probable that a current the efficiency of which could be governed by 
the number of interruptions of the primary circuit as well as by the 
position of the secondary coil, could be made to give more constant 
results and at the same time admit of finer gradations. To obtain 
such a current the primary circuit of an ordinary Du Bois-Beymond 
induction coil was interrupted by an “ oscillating rod ” kept in vibra- 
tion by an electro-magnet, the number of interruptions per second 
being determined by the length of the rod set into vibration. The 
vibrations were recorded upon a drum kymograph by means of a 
Desprez signal; a pen marking seconds wrote directly beneath this, 
so that the rate of vibration could be read off at any time. Three to 
nine double vibrations per second were found sufficient as a rule. By 
altering the number of interruptions of the primary circuit and chang- 
ing the position of the secondary coil, the desired effect upon the 
heart could be produced when the vagus was stimulated; and it was 
found that this effect remained very constant during a number of 
succeeding stimulations as well as during a long-continued stimulation 
of the vagus. Numerous examples of the effect of stimulating the 
vagus in this manner for short periods (ten to fifteen seconds) will 
be given later; here the results of a stimulation continuing for some 
time will be described. 
Effect upon the heart of a long-continued stimulation of the vagus 
with the slowly interrupted current.—During the course of a more or lleid Hunt 
155 
less prolonged stimulation of the vagus in this manner slight changes 
in the rate of the heart occurred; the most common of these was a 
slight escape soon after the beginning of the stimulation. Hough* 
has recently described such an escape when the heart was slowed 
slightly by stimulating the vagus with the ordinary rapidly interrupted 
current. Judging from Hough’s account, I think the escape occurs 
less frequently and is less complete when the slowly interrupted cur- 
rent is used; indeed, in some cases no escape whatever occurred, and 
in others, sometimes with, sometimes without a slight escape at the 
beginning, the rate of the heart decreased slightly but regularly as 
the stimulation continued. The following experiments will illustrate 
these points. 
1. Cat. Ether anaesthesia. Vagi and accelerators cut. Peripheral 
end of 1. vagus stimulated by current interrupted nearly 4 times per 
second; secondary coil 12 cm. 
Time. 
* 
Heart-beats In 
Blood- 
hr. 
min. 
sec. 
10 seconds. 
pressure. 
3 
53 
50 
40 
107 mm. 
54 
30 % 
90+ 
Stimulus on vagus. 
10 
28+ 
83+ 
• 
20 
28+ 
77 
30 
28%+ 
74 
40 
29- 
71+ 
50 
29 
68 
55 
30% 
64+ 
56 
32% 
65+ 
57 
32 
65 
58 
32 
64 
4 
1 
Stimulus off vagus. 
4 
1 
10 
40% 
99 
2. Cat. Ether. Vagi and accelerators cut. L. vagus; 4 interruptions 
per second; secondary coil 9 cm. 
Heart-beats in 
hr. 
min. 
sec. 
10 seconds. 
3 
30 
30 
is y» 
40 
17 
Stimulus on vagus. 
50 
14+ 
31 
15- 
10 
15 
20 
15 + 
32 
15+ 
33 
isy,- 
* Hough, Journal of Physiology, xviii, p. 161, 1895 156 
Relation of Inhibitory to Accelerator Nerves of Heart 
The above experiments have been selected especially to illustrate 
the fact that the heart escapes from weak stimulation of the vagus 
after section of the accelerators. 
3. Bitch. Morphine and ether, curare. Vagi cut; accelerators intact. 
R. vagus; 5§ interruptions of primary circuit per second; secondary coil 
0 cm. 
Heart-beats in 
Blood- 
hr. 
min. 
sec. 
10 seconds. 
pressure. 
2 
24 
40 
50 
70 mm. 
50 
33+ 
67 
Stimulus on vagus. 
25 
32+ 
63+ 
10 
33+ 
63+ 
20 
35% 
63 
26 
35% 
60 
30 
35% 
59+ 
40 
45% 
67 
Stimulus off vagus. 
27 
49% 
69 
The accelerators were now cut and the vagus again stimulated with 
the same strength of current. 
Heart-heats in 
Blood- 
hr. min. 
sec. 
10 seconds. 
pressure. 
2 46 
10 
32% 
56 mm. 
20 
22 
44 
Stimulus on vagus. 
30 
20% + 
41 
40 
20%- 
38 
50 
20%~ 
37 
47 
20 %- 
37 
48 
20%- 
39 
49 
20- 
41 
50 
19% ~ 
42 
51 
18+ 
43 
52 
18- 
43 
56 
10 
35+ 
• 
Stimulus off vagus, 
The second of the foregoing tables illustrates the gradual slowing 
of the heart which sometimes occurs during the course of a prolonged 
stimulation of the vagus; such results, as well as the entire absence 
of escape, have been observed most frequently after section of the 
accelerator nerves, but not exclusively then, as the following shows. 
4. Rabbit. Morphine and chloral. Vagi cut. Accelerators intact. 
L. vagus stimulated; secondary coil at 20 cm.; about 4-| interruptions 
of the primary circuit per second. Reid Hunt 
157 
Heart-beats In 
Blood - 
hr. 
min. 
sec. 
10 seconds. 
pressure. 
4 
2 
30 
28%" 
51 mm. 
40 
26+ 
48 
Stimulus on vagus. 
50 
25+ 
48 
3 
25+ 
48 
30 
25 + 
48 
4 
25 
48 
5 
25- 
48 
6 
24+ 
48 
7 
23% 
48 
8 
23 
48 
10 
23 
48 
12 
23 
48 
14 
23 
48 
16 
22% 
48 
•17 
21% 
47 
18 
10 
24+ 
48 
Stimulus off vagus. 
19 
26- 
50 
Another point of interest in this connection is the fact that when 
the vagus is stimulated in the course of a prolonged stimulation of 
the accelerators, the heart escapes just as when the vagus is stimulated 
alone; an experiment illustrating this will be described in the latter 
part of this paper. 
Effect of section of the accelerators upon the result of stimulating 
the vagus.—My experiments have not been sufficiently numerous or the 
results sufficiently constant to admit of very positive statements upon 
this point. In addition to the fact noted above that in general the 
escape of the heart from slowing produced by stimulation of the vagus 
seems to be less complete after section of the accelerators, the effect 
of the stimulation seems to be greater, as described long ago by 
Sustschinsky.* Thus in the above-quoted experiment upon the dog the 
maximum slowing before section of the accelerators was 36 per cent; 
after their section it was 50.7 per cent, when the same strength of 
current was used. Ho special attention, however, has been given to 
this point. Reflex stimulation of tlje vagus is much more effective 
after section of the accelerators; this point, however, will be discussed 
in a later paper. 
* Sustschinsky, Unters. aus dem physiol. Laborat. in Wurzburg, iii, p. 164, 1868. 158 
Relation of Inhibitory to Accelerator Nerves of Heart 
Part III. 
STIMULATION OF THE ACCELERATOR NERVES. 
Effect upon the heart rate of cutting the accelerators.—In most of 
my experiments all the nerves going to the stellate ganglia, except the 
ventral limb of the annulus of Vieussens, were cut; this gave an 
opportunity of making observations upon the question of the tonic 
activity of the accelerator nerves, the evidence for which seems to be 
accumulating.* The ganglia were thoroughly exposed by opening 
the thorax and resecting the first ribs some time before the nerves 
were cut. With the ganglia thus exposed, it was very easy to cut 
all their connections without doing any injury to surrounding parts, 
so that the possibility of causing a reflex slowing of the heart through 
the vagi, in case these were not cut, was much diminished. In almost 
every case removal of the stellate ganglia caused a considerable de- 
crease in the heart rate whether the vagi were cut or were intact. 
This is well shown in the experiment upon the dog already quoted 
(p. 156). 
hr. min. 
Heart-beats in 
10 seconds. 
Blood- 
pressure. 
to 
to 
00 
49 
71 mm. 
29 
E. stellate ganglion cut out. 
30 
41+ 
66 
40 
L. stellate ganglion cut out. 
43 
33 
52 
A point of interest not well shown in the above experiment is the 
difference almost always observed in the result of removing the right 
and left ganglia. In almost every experiment removal of the right 
ganglion caused a considerable slowing of the heart with little effect 
upon the blood pressure, while removal of the left had less effect 
upon the heart rate and more effect upon the blood pressure. This 
occurred whichever ganglion was removed first, and whether the vagi 
were cut or intact. A rather extreme case is the following: 
* Timofeew, Centralblatt f. Physiologic, 1889, p. 235. Strieker and Wagner, 
Wien, medizinische Jahrbucher, 1878, p. 370. Reid Hunt 
159 
Dog. Morphine and ether. Vagi intact. 
Heart-rate in 
Blood- 
hr. 
min. 
sec. 
10 seconds. 
pressure. 
1 
20 
32 % 
108 mm, 
25 
It. stellate ganglion cut out. 
25 
10 
31 
20 
30+ 
30 
30- 
40 
29 
50 
28- 
26 
26+ 
10 
24+ 
20 
24- 
30 
23% 
40 
23 
50 
22% 
28 
22 
103 
2 
4 
18 
103 
6 
L. stellate ganglion cut out. 
8 
18- 
60 
It will be shown in the next section that stimulation of the right 
annulus of Vieussens in these cases had a much more marked effect 
in accelerating the heart than did that of the left; this fact taken 
with the above seems to indicate that more accelerator fibres pass 
from the right stellate ganglion than from the left. 
Similar results were obtained with cats, as is shown in the following: 
Cat. Ether. E. vagus cut. 
hr. 
min. 
Heart-beats In Blood- 
10 seconds. pressure. 
11 
51 
37 106 mm. 
53 
L. stellate ganglion extirpated 
55 
36 98 
12 
24 
35 114 
26 
R. stellate ganglion extirpated. 
29 
28+ 109 
Such experiments would seem to indicate that the accelerator centre 
is in tonic activity, but the possibility that the centre had been stimu- 
lated in some manner, as, e. g., by the anaesthetics used—morphine and 
ether in the case of the dog, ether in the case of the cat—(just as 
morphine is known to stimulate the cardio-inhibitory centre*) must be 
remembered. In fact the excessively rapid heart often observed 
* Gscheidlen, JJnters. avs dem physiol. Laborat. in Wiirzburg, iii, p. 15. 1868. 160 
Relation of Inhibitory to Accelerator Nerves of Heart 
after section of the vagi in dogs under the influence of morphine 
is very suggestive of such an action on the part of this drug, 
but I know of no experiments bearing upon this point. On the 
other hand this result, viz., slowing of the heart after section of the 
accelerators, has been observed under such various conditions and 
when no drug had been used ( e. g., when anaesthesia was produced by 
section of the crura cerebri) that I am inclined to accept the view that 
the accelerator centre is usually in tonic activity. In a few experi- 
ments it was impossible to cause, by stimulation of the accelerators, a 
greater frequency of the heart beat than existed before section of these 
nerves; apparently in such cases the accelerators had been in a state 
of maximal activity when they were cut. 
One thing is certain, the slowing of the heart following section of 
the accelerators in these experiments cannot be referred to a reflex 
action through the vagus, for it occurred as often in animals in which 
the vagi had been cut or had been paralyzed by atropine as in those 
in which the vagi were intact; indeed it occurred more frequently in 
those in which the vagi were cut, a fact which I think can be ex- 
plained by the following observation: All my experiments go to show 
that in properly anaesthetized animals, operative procedures tend to 
cause a diminution of the tonic activity of the cardio-inhibitory centre 
rather than to increase it. This is especially marked in dogs under 
the influence of morphine, upon which so many of my experiments 
were performed; in such animals I have repeatedly observed an in- 
crease of the heart rate, continuing often for several minutes, to 
follow such an operation as cutting the sciatic nerve, and as this has 
occurred in animals in which the stellate ganglia were completely 
removed, it can be explained only by supposing the tonic activity 
of the vagus centre to have been diminished. What appears to be a 
similar thing occurred in a few of my experiments upon the accelera- 
tors; thus in one the vagi were intact and the heart was beating at the 
rate of 43 beats in 15 seconds; the extirpation of the stellate ganglia 
caused an increase in the heart rate of 9 beats in 15 seconds, and this 
rate was but slightly increased by the subsequent division of the vagi. 
The manner in which the slowing following section of the accelera- Reid Hunt 
161 
tars occurred is interesting; it did not occur immediately upon section 
of the nerves, but developed gradually in the course of a period vary- 
ing from one to several minutes. In other words the slowing of the 
heart from section of the accelerators is strikingly like the return of 
the heart rate to the normal after stimulation of these nerves. The 
second of the experiments described above illustrates this point very 
well. 
Stimulation of the accelerators.—The accelerator nerves were stimu- 
lated in various parts of their course. In the dog those fibres running 
in the ventral limb of the annulus of Yieussens were usually stimu- 
lated; at times, however, the stimulus was applied to the rami com- 
municantes passing to the stellate ganglion or to the small nerves 
given off from the annulus or the inferior cervical ganglion. In the 
cat the “ nervus accelerans,” as described by Boehm,* was stimulated. 
There was seldom any difficulty in obtaining a marked acceleration 
of the heart when any of the above nerves was stimulated on the right 
side. The percentage of acceleration varied greatly in different 
experiments; the maximum effect I observed was an increase from 
16 to 32 beats in 10 seconds, or an acceleration of 100 per cent. 
Stimulation of these nerves on the left side in both dogs and cats 
has almost always in my experiments been much less effective than 
that of the nerves on the right side. Thus in the experiment recorded 
on page 159, stimulation of the right annulus caused an increase in the 
heart rate from 19 to 30 beats in 10 seconds, or an acceleration of 
nearly 58 per cent, while stimulation of the left annulus and of the 
rami communicantes passing to the left stellate ganglion caused a 
slight rise of blood pressure, but no’change in the heart rate. 
Occasionally a slowing of the heart, sometimes with, sometimes 
without a succeeding acceleration, resulted from the stimulation of 
the annulus; this occurred especially frequently when the left annulus 
was the one stimulated. Roy and Adami f describe results similar to 
these and suggest that they may be due to the stimulation of vaso- 
constrictor nerves of the coronary vessels. In some of my experi- 
* Boehm, Arch. f. exp. Pathol, u. Pharmakol., iv, p. 256, 1875. 
f Roy and Adami, Phil. Trans., clxxxiii B, p. 294, 1892. 162 
Relation of Inhibitory to Accelerator Nerves of Heart 
ments this slowing was evidently a reflex effect through the vagi, for 
it could no longer be obtained when the vagi were cut. That afferent 
nerves may pass through the ventral branch of the annulus (especially 
on the left side) is shown by the fact that when this is stimulated, 
reflex movements of the legs and of the respiratory muscles sometimes 
occur; section of the vagi prevents the recurrence of these reflexes. 
Stimulation of the accelerators after section of the vagi.—Since the 
vagi are usually in tonic activity, especially in dogs, we should expect 
to find the maximum to which the heart can be accelerated by weak 
stimulation of the accelerators to be greater after section of the vagi 
than before, that is if we assume that the two nerves are antagonistic. 
A few of my experiments indicate that this is the case, and I think 
it not improbable that the reason the others do not is due to the fact 
that the stimulus used was sufficiently strong to overcome completely 
the action of the vagi, and consequently the maximum rate was the 
same before as after section of the vagi. The “ after-effect ” of the 
stimulation of the accelerators, however, is markedly prolonged by 
the section of the vagi. 
Since section of the vagi causes an increase in the heart rate, the 
percentage of acceleration from stimulating the accelerators is less 
after than before the vagi are cut. Still in such cases I have found 
no difficulty in obtaining an acceleration varying from 10 to 63 per 
cent. An acceleration has also been obtained after the administration 
of atropine till stimulation of the peripheral end of the vagus no longer 
caused a slowing of the heart. 
Such experiments as the above corroborate the results of others, 
and show how incorrect is the statement, recently made,* that after 
section of the vagi or the administration of atropine no increase in 
the heart rate can be caused by stimulation of the accelerators. 
* Eoy and Adami, op. cit., pp. 267 and 296. These authors describe, never- 
theless (p. 246), an experiment in which stimulation of the left annulus 
caused an increase in the heart rate from 17 to 24 y2 beats in 10 seconds, 
after the vagus had been completely paralyzed by atropine. Reid Hunt 
163 
Part IV. 
SIMULTANEOUS STIMULATION OF THE VAGUS AND THE ACCELERATORS. 
The results of these experiments will be described under three 
heads: (1) stimulation of the accelerators during a prolonged stimu- 
lation of the vagus, (2) stimulation of the vagus during a prolonged 
stimulation of the accelerators, and (3) stimulation of the two nerves 
begun at the same time. 
1. 
Stimulation of the Accelerators during a Prolonged Stimulation 
of the Vagus. 
This phase of the subject does not seem to have been considered by 
Baxt. Bearing in mind, however, the great uniformity of the results 
obtained in a long-continued stimulation of the vagus, this method 
seems especially adapted to the solution of the problem of the rela- 
tion of the two nerves. 
The following experiment is a good illustration of what has invari- 
ably occurred: 
Dog. Morphine and ether; curare. Vagi and accelerators cut. R. 
vagus stimulated; secondary coil at 0 cm.; primary circuit interrupted 5| 
times per second. R. annulus stimulated; secondary coil 10 cm. 
Heart-beats in 
hr. min. 
sec. 
15 seconds. 
Remarks. 
2 46 
15 
49 % 
Stimulation of vagus begun. 
47 
31 %- 
51 
27+ 
Maximal slowing 43.2%. 
52 
28 
15 
58 
K. annulus stimulated for 15 
seconds. 
30 
58% 
Acceleration of 108.9%, or 
18.1% above the normal rate. 
45 
44% 
53 
40% 
56 
39- 
Stimulus off vagus. 
30 
54% 
The stimulus was taken off the vagus while the after-effect of the 
stimulation of the accelerators was still evident. 164 
Relation of Inhibitory to Accelerator Nerves of Heart 
The accelerators were now stimulated alone with the same strength 
of current as was used in the above. The results wrere as follows: 
Heart-beats In 
hr. 
min. 
sec. 
15 seconds. 
Remarks. 
2 
58 
30 
53+ 
45 
75% 
K. annulus stimulated for 15 
seconds. 
59 
77 
Acceleration of 45.3%. 
3 
63 
2 
60 
These results are shown in the plotted curves in Tig. 1 
Fig. 1.—Stimulation of the accelerators during a prolonged stimulation 
of the vagus. The ordinates represent the heart rate in 15 seconds; the 
abscissae the time in minutes. 
A. The vagus was stimulated from V to v (10 minutes); the accelerators 
from a to a (15 seconds). 
B. Stimulation of the accelerators alone (15 seconds). 
Comment on these figures is scarcely necessary. They show that 
a stimulation of the vagus of sufficient strength to cause a decrease of 
the heart rate of 43.2 per cent is not only completely overcome by a 
stimulation of the accelerators, but that the latter causes an accelera- 
tion of 18.1 per cent above the rate at which the heart was beating Reid Hunt 
165 
before the vagi were stimulated and an actual acceleration of 108.9 
per cent. That the effect of the vagus on the other hand was not 
lost is shown by the fact that the maximum rate reached while both 
nerves were stimulated was but 58-| beats in 15 seconds as compared 
with 77 when the accelerators alone were stimulated; or while the 
acceleration above the normal rate was but 18.1 per cent in the former 
case, it was 45.3 per cent in the latter. 
It might be thought that if the vagus and accelerators are purely 
antagonistic, a stimulation of the accelerators of sufficient strength to 
cause an acceleration of 45 per cent would just neutralize the effect 
of the vagus or cause but a very slight acceleration above the normal 
when the vagus was being stimulated with a current of sufficient 
strength to cause a slowing of 43 per cent, while in this experiment 
there was an acceleration of 18 per cent. However, it must be remem- 
bered that in general a slowly beating heart is more powerfully influ- 
enced by a stimulation of the accelerators than is one beating more 
rapidly; moreover, there are so many other factors entering into the 
problem that we could scarcely expect the result to be the exact alge- 
braic sum of the results of the separate stimulations. 
Results similar to the above have been obtained in experiments 
upon cats,* as the following table will show. 
Cat. Ether. Vagi and accelerators cut. L. vagus stimulated; 4 in- 
terruptions per second of primary circuit; secondary coil 10 cm. R. 
annulus stimulated; secondary coil 11 cm. 
Heart-beats in 
hr. 
min. 
sec. 
20 seconds. 
Bemarks. 
2 
53 
20 
42 
40 
23 
Stimulation of vagus begun. 
54 
20% 
55 
29 
56 
30 
Heart slowed 28.5%. 
20 
45% 
Accelerators stimulated for 20 
seconds. 
40 
38 
Acceleration of 51.6% 
57 
34 
58 
30% 
4 
2 
30 
23 
30 
Stimulus off vagus. 
20 
38 
* Dr. D. W. Harrington and I have since obtained similar results in an 
experiment upon an opossum. 166 
Relation of Inhibitory to Accelerator Nerves of Heart 
2. 
Stimulation of the Vagus during a Prolonged Stimulation of the 
Accelerators. 
The following experiments will serve to illustrate this side of the 
subject; a somewhat similar experiment wrill be described in the next 
section of this paper. 
Young dog. Morphine and ether; curare. Vagi and accelerators cut. 
R. vagus stimulated; primary circuit interrupted 3f times per second; 
secondary coil at 4, later at 5 cm. L. annulus stimulated with ordinary 
induced current; secondary coil 15 cm. The vagus was first stimulated 
alone twice for the purpose of comparison. 
Heart-beats in 
hr. min. 
sec. 
16 seconds. 
lie marks. 
12 35 
48- 
41 % 
Vagus stimulated 15 seconds; 
coil 5 cm. 
37 
47 
40- 
Vagus stimulated 15 seconds; 
coil 4 cm. 
41 
46 
15 
57 
Stimulation of accelerators 
begun. 
30 
56 
45 
55+ 
42 
46- 
Vagus stimulated 15 seconds; 
coil 4 cm. 
15 
54+ 
43 
54 
15 
48 
Vagus stimulated 15 seconds; 
coil 5 cm. 
30 
52 % + 
46 
53 y2 
15 
46 
Vagus stimulated 15 seconds; 
coil 4 cm. 
30 
52+ 
47 
53 
15 
47 
Vagus stimulated 15 seconds; 
coil 5 cm. 
48 
53+ Reid Hunt 
167 
Some of these results are shown in Fig. 2. 
Fig. 2.—Stimulation of the vagus during a prolonged stimulation of the 
accelerators. 
A. Stimulation of the vagus alone (15 seconds). 
B. The accelerators were stimulated from a to a (9 minutes); the vagus 
was stimulated twice (at v and v') for 15 seconds. 
The first stimulation of the vagus in this experiment just overcame 
the effect of the stimulation of the accelerators and the heart was 
brought back to its normal rate; that the accelerator effect was not 
lost, however, is shown by comparing the rate of the heart when the 
vagus alone was stimulated (not quite 40 beats in 15 seconds) with 
that when both nerves were being stimulated (46 beats in 15 seconds). 
Stimulation of the vagus a second time, with a weaker current, caused 
a diminution of the accelerator effect, but the heart was not brought 
back to its normal rate. The two subsequent stimulations of the 
vagus show how constant were these results. 
3. 
Stimulation of the Vagus and Accelerators begun simultaneously. 
The results of stimulating the two nerves simultaneously (a) for 
short periods (ten to fifteen seconds) and (b) for longer periods (sev- 
eral minutes) will be described in this section. 
a. Simultaneous stimulation of the vagus and accelerators for short 
periods. — Experiments will be described first in which the vagus was 168 
Relation of Inhibitory to Accelerator Nerves of Heart 
stimulated with the slowly interrupted current, and the accelerators 
with the ordinary rapidly interrupted current. Each nerve was fre- 
quently stimulated alone to obtain figures for comparison. The results 
are arranged in the form of tables. In the first column is given the 
time; in the second, the nerve or nerves stimulated; in the third, the 
duration of the stimulation; in the fourth, the number of heart beats 
(d) during the stimulation, (b) in the interval corresponding to the 
duration of the stimulation immediately preceding, and (a) the number 
in the interval immediately following the stimulation; in the last 
column is given the change in the heart rate in per cent, the minus 
sign indicating a slowing and the plus sign an acceleration. 
Dog. Morphine and ether; curare. Vagi and accelerators cut. 
hr. min. sec. 
seconds. 
b. 
d. 
a. 
5 2 
40 
R. vagus; coil 0 cm.; 
4% interruptions per 
second. 
15 
35 
45 
-26.4% 
5 
30 
II. annulus; coil 12 cm. 
15 
45- 
51% 
56% 
+21.1% 
8 
10 
Both nerves; coils, etc., 
as above. 
15 
47 
44 
55 
-6.3% 
These results are shown more satisfactorily in Fig. 3, in which the 
heart beats are given in periods of 5 seconds. 
Figs. 3 and 4.—Stimulation of the vagus and accelerators begun simul- 
taneously. The ordinates represent the heart rate in 5 seconds; the abscissae 
the time in intervals of 10 seconds; “ a ” stimulation of the accelerators 
alone; stimulation of the vagus alone; “ a v ” stimulation of the two 
nerves simultaneously. The stimulations continued in each case for 15 
seconds (from s to s) and followed each other at short intervals. The 
strength of the current was different in the two cases. Reid Hunt 
169 
In this case the figures representing the result of stimulating the 
two nerves simultaneously are not far from being the algebraic sum 
of the figures obtained when the two were stimulated separately. 
These figures show conclusively that neither nerve has overcome the 
effect produced by the other; both have made their influence felt and 
to almost equal degrees, the inhibitory effect slightly predominating. 
After the stimulation the accelerator effect appeared to almost the 
same extent as when this nerve was stimulated alone, as was described 
by Baxt. This latter fact is readily understood when we remember 
that the accelerators have a long after-effect, while the vagus has not. 
The results of a few subsequent stimulations made in the same 
experiment will be given to illustrate the effect of altering the strength 
of the stimuli. In the first table it will be observed that the number 
of vibrations per second of the oscillating rod was increased. 
hr. min. sec. 
seconds. 
b. 
d. a. 
5 50 
R. vagus; coil 0 cm.; 
5£ vibrations per 
second. 
15 
49% 
33% 
-32.3% 
51 
Vagus; coil, etc., as 
above. R. annulus; 
coil 12 cm. 
15 
49% 
37 56 
-25.2% 
The current by which the annulus was stimulated was now strength- 
ened by moving the secondary coil up to 10 and then to 8 cm. 
hr. min. sec. 
seconds. 
b. 
d. 
a. 
5 52 30 
Vagus (as before). R. 15 
annulus; coil 10 cm. 
49 
44% 
56 
-9.1% 
54 30 
Vagus (as before). R. 15 
annulus; coil 8 cm. 
51 
44 
56 
-13.7% 
The vagus effect still predominated, though to a less degree. It 
will be observed that the second increase of strength in the stimulus 
applied to the accelerators did not cause, a corresponding increase in 
the effect upon the heart; such irregularities frequently occurred, but 
still the effect of the stimulation of the accelerators is plainly seen if 
the rate of the heart during the stimulation of the vagus alone 
beats in 15 seconds) is compared with that during the stimulation of 
the two nerves (44 in 15 seconds). 
The current by which the vagus was stimulated was weakened by 170 
Relation of Inhibitory to Accelerator Nerves of Heart 
diminishing the rate of the oscillating rod, and now the accelerators 
slightly predominated, as is shown in the following: 
hr. min. sec. 
seconds. 
b. 
d. 
a. 
5 57 
R. annulus; coil 8 cm. 
15 
52 
54 
57% 
+3.8% 
R. vagus; coil 0 cm.; 
3y2 interruptions. 
59 
R. vagus (as above). 
15 
52 
47 
48% 
-10.0% 
6 5 
R. annulus; coil 8 cm. 
15 
51% 
57 
58 
+ 10.6% 
These results are shown in Fig. 4 (p. 168). 
In the foregoing experiment there was a tendency for the inhi- 
bitory effect to predominate; in the following the tendency was rather 
for the accelerator effect to be more marked. 
Small bitch. Morphine and ether; curare. Vagi and accelerators cut. 
hr. min. sec. 
seconds. 
b. 
d. a. 
3 49 
R. annulus; coil 14 cm. 
15 
34% 
44 47 
+27.5% 
52 
L. vagus; coil 5 cm.; 
3% interruptions per 
second. 
15 
33% 
25 
-25.3% 
59 
Both nerves; coils, 
etc., as above. 
15 
32% 
35% 
+9.2% 
The stimulus for the vagus was now made stronger and the nerves 
again stimulated. 
hr. min. sec. 
seconds. b. 
d. 
a. 
4 3 
R. annulus; coil 14 cm. 15 34- 
L.vagus; coil 4 cm.; 
3% interruptions per 
second. 
34 y2 
46 
, +4.4% 
The current by which the accelerators were stimulated was now weak- 
ened, but one of the above-mentioned irregularities occurred. 
hr. 
min. sec. 
seconds. 
b. 
d. 
a. 
4 
7 
L. vagus; coil, etc., as 
. above. R. annulus; 
coil 16 cm. 
15 
32 % 
37% 
45% 
+ 15.4% 
4 
10 
Vagus (as above). 
15 
33- 
25+ 
-24.2% 
4 
15 
Vagus (as above). R. 
annulus; coil 17 cm. 
15 
31 
30%+ 
43% + 
-1.0% 
These tables show that when the stimuli applied to the two nerves 
are properly selected, the effect of one nerve can be made exactly to Reid Hunt 
171 
counterbalance that of the other. Similar figures could be given 
from many other experiments. Irregularities, such as were pointed 
out above, frequently occurred when the results of the use of stimuli 
of different strengths were compared with each other; but all the 
experiments, without a single exception, lead to the same conclusion, 
viz., that when the two nerves are stimulated simultaneously with 
stimuli at all comparable in strength (as judged by their separate 
effects upon the heart), the effect of each is plainly visible during the 
stimulation; the stimulation of one has never caused the complete 
obliteration of the effect of stimulating the other. If, however, the 
stimulation of one nerve is very strong in comparison with that of 
the other, then its effect alone may appear. This is sufficiently well 
known when the vagus is stimulated with a strong current; the follow- 
ing experiment shows that the reverse may occur, namely, the accele- 
rator effect alone appear. 
Dog. Morphine and ether. Accelerators cut. R. vagus intact. Cen- 
tral end of 1. vagus stimulated with the ordinary induced current, and 
the heart thus slowed reflexly. The accelerators were stimulated with 
the slowly interrupted current. 
Heart-beats. 
Change 
hr. rain. sec. 
Duration of ,— 
stimulation, b. 
d. 
of heart 
rate in %. 
3 44 
Vagus; coil 10 cm. 
20 sec. 52 
47% 
-8.6% 
47 
K. annulus; coil 5 cm.; 
20 54 
67% 
+25.0% 
50 
3f interruptions per 
second. 
Both nerves; coils, 
20 55 
69% 
+26.4% 
52 30 
etc., as above. 
Vagus; coil 10 cm. 
20 57 
48% 
-14.9% 
Later in this experiment the peripheral end of the vagus was stimu- 
lated with the ordinary rapidly interrupted current and the accelera- 
tors with the slowly interrupted current; as the following figures 
show, the results are the same as when the methods of stimulation 
were reversed, as was the case in the experiments previously quoted. 
The slowly interrupted current was usually used to stimulate the 
vagus only because it seemed to give, as a rule, more constant results. 172 
Relation of Inhibitory to Accelerator Nerves of Heart 
hr. min. sec. 
Duration of 
stimulation. 
b. 
Heart-beats. 
d. 
a. 
Change 
of heart 
rate In %. 
4 10 
L. vagus; coil 21 cm. 
15 sec. 
39 
34% 
37% 
“11.5% 
11 30 
L. vagus; coil 21 cm. 
15 
38 
41+ 
48 
+7.9% 
13 
Ii. annulus; coil 5 
cm.; 3% interrup- 
tions per second. 
L. vagus; coil 21 cm. 
15 
37 
33 
37 
-10.8% 
15 
Both nerves; coils, 
15 
36% 
42 
46% 
+ 15.3% 
17 
etc., as above. 
L. vagus; coil 21 cm. 
15 
37% 
34+ 
37 
-9.3% 
19 
Annulus (as above). 
15 
36% 
46% 
49 
+27.4% 
21 
Both nerves; coils, 
15 
37- 
44+ 
46% 
+ 18.9% 
23 
etc., as above. 
Vagus; coil 21 cm. 
15 
36 
34% 
35% 
-6.9% 
During these stimulations the irritability of the inhibitory nerves 
seemed to decrease, that of the accelerators to increase. 
(b). Simultaneous stimulation of the vagus and accelerators continu- 
ing for some time.—Having found that when the two nerves are 
stimulated together for short periods, the elfect of either can be neu- 
tralized by that of the other, so that the rate of the heart is scarcely 
affected, the effect of stimulating both for a longer period was tried. 
As was pointed out at the beginning of this paper, however, this 
problem is somewhat different from the one we have been discussing, 
for now the possibility of the exhaustion of one or the other of the 
nerves must be considered. It is well known that the heart can be 
kept beating at a very slow rate for many hours by stimulating the 
vagus; I have been unable to find references to any experiments bear- 
ing upon the question of the fatigue of the accelerator nerves in 
mammals. Boehm,* it is true, says it is doubtful whether these 
nerves can be fatigued at all; but he does not seem to have stimulated 
them for periods longer than two minutes, and he is certainly not jus- 
tified in drawing such a conclusion from stimulations of so short a 
duration. 
I have performed a large number of experiments in order to deter- 
mine how easily the accelerators are fatigued, or whether they are 
fatigued at all; the results of these experiments I hope soon to publish 
in full. Although these results are complicated and difficult to in- 
terpret, I think the following general conclusions may be drawn from 
them. When a moderately strong stimulus is applied to the accele- 
* Boehm, loc. cit. Keid Hunt 
173 
rators the rate of the heart rapidly rises to a maximum and remains 
at this level for a very variable period, occasionally for 8 or 10 minutes, 
but usually for a much briefer period. The rate then decreases, 
at first very rapidly and then very slowly; in many cases it reaches 
an almost constant level, which it may maintain as long as the stimu- 
lation continues. Frequently this constant level has almost coincided 
with the rate at which the heart was beating before section of the 
nerves, and this may be taken to represent the normal rate of the heart. 
The rate reached during a long-continued stimulation of the accele- 
rators has seldom, if ever, in my experiments remained greater than 
the normal (using “ normal ” as above); usually it has been less, 
though still greater than that at which the heart was beating imme- 
diately before the stimulation began. 
The fact that the heart can, by stimulating the accelerators, be 
maintained at its maximum rate for but a very short time might be 
attributed either to fatigue occurring in the cardiac muscle or in the 
endings of the nerves, or, as Professor Howell suggested, to a local 
effect upon the nerve at the point stimulated, that is, to what Pro- 
fessor Howell has called “stimulation fatigue.”* In fact both of 
these factors seem to be involved; there is undoubtedly a local effect 
upon the nerve at the point stimulated which is the first cause of the 
decrease of the heart rate, but there also seems to be distinct evidence, 
which will be presented in a future paper, of fatigue occurring in 
the heart itself. 
In any case the heart cannot be kept in a condition of maximum 
acceleration or beating at a rate much above what we may consider 
the normal rate for more than a very few minutes, offering in this 
respect a marked contrast to its conduct upon stimulation of the vagus. 
What will be the final result of stimulating the two nerves together 
for a long period ? Will the accelerators become completely exhausted 
and then the result be as if they were not being stimulated at all and 
the vagus exert its full influence? It is evident that the answers to 
these questions have interesting bearings upon the problem as to the 
manner in which the nerves affect the heart, and especially upon 
Gaskell’s theory of the metabolic functions of these nerves. I hope 
* Howell, Budgett and Leonard, Journal of Physiology, xvi, p. 311, 1894. 174 
Relation of Inhibitory to Accelerator Nerves of Heart 
to investigate this question more fully in the near future, hut will 
give here a few figures from experiments bearing upon it. In these 
experiments the local effect of the stimulus on the accelerators is 
disregarded, "which I think may be done without affecting the general 
conclusions. In the first experiment recorded below the accelerators 
had been stimulated several times earlier in the experiment, so that 
they were probably more easily fatigued than they would otherwise 
have been. 
Bitch. Morphine and ether; curare. Vagi and accelerators cut. R. 
vagus stimulated by slowly interrupted current; secondary coil 0 cm.; 
7 interruptions per second of the primary circuit. R. annulus of Vieus- 
sens stimulated with the ordinary rapidly interrupted current; secondary 
coil at 15, then at 17 cm. 
Hearts-heats In 
hr. min. 
sec. 
10 seconds. 
Remarks. 
3 19 
30 
46 
40 
37 
Stimulation of vagus begun. 
50 
34 
20 
33 + 
21 
34 % 
40 
34% 
50 
Stimulation of accelerators 
begun. 
22 
51 
23 
49- 
24 
47 + 
26 
45% — 
28 
45% — 
30 
45— 
31 
44+ 
33 
43 
34 
42% 
Stimulus off annulus. 
35 
37% 
36 
36+ 
38 
35- 
10 
43% 
Stimulation of annulus be- 
gun; coil 17 cm 
20 
47% 
30 
48 
39 
45 
40 
44 
42 
42% 
43 
10 
41% 
Stimulus off annulus. 
20 
36% + 
45 
45 + Reid Hunt 
175 
Fig. 5.—Long-continued stimulation of the vagus and accelerators. The ordinates represent the heart rate in 10 seconds; the 
abscissae, the time in minutes. The vagus was stimulated from v to v (25 minutes); the accelerators were stimulated twice— 
from a1 to a1 (12% minutes) and from o* to o* (9 minutes). 
We see that in this experiment 
when the two nerves were stimu- 
lated together neither completely 
overcame the effect of the other 
in 12£ minutes, though the vagus 
gradually decreased the effect of 
the accelerators. That the effect 
of the stimulation of the accel- 
erators was not completely over- 
come is shown by the fact that 
the heart rate is greater during 
the combined stimulation than 
during that of the vagus alone; 
also when the stimulation of the 
accelerators wTas discontinued, the 
heart rate quickly fell to what it 
had been under the influence of 
the vagus alone. It will be 
noticed that during the stimula- 
tion of the two nerves the heart 
rate fell below what it had been 
before the stimulation began; 
what the result would have been 
had the stimulation continued 
still longer it is impossible to say. 
(See Fig. 5.) 
In the following experiment 
the nerves were stimulated to- 
gether for more than half an 
hour. Changes in the condition 
of the animal almost necessarily 
occurred in such a long time; the 
depth of the anaesthesia and the 
temperature of the animal doubt- 
less varied. The blood pressure 
fell and the heart was beating 
more slowly after than before the 
stimulation. The results, how- 
ever, are interesting and very 
suggestive. 176 
Relation of Inhibitory to Accelerator Nerves of Heart 
Bitch. Morphine and ether; curare. Vagi and accelerators cut. R. 
vagus stimulated; secondary coil 2 cm.; primary circuit interrupted 4 
times per second. R. annulus stimulated; coil 15 cm. Several stimula- 
tions of the annulus had preceded the one described here. 
Heart-beats in 
hr. 
miu. 
see. 
15 seconds. 
Remarks. 
12 
20 
45 
61 
21 
68 
Stimulation of accelerators 
begun. 
15 
70 
45 
67 
22 
56 
Stimulation of vagus begun. 
15 
52% 
30 
46 
45 
56 
24 
57% 
26 
57% 
28 
57 
30 
57 
32 
56% 
36 
56 
38 
55- 
40 
54%— 
42 
53% 
44 
54 
46 
53% 
50 
53% + 
52 
54 
53 
54+ 
55 
53% 
Stimulus off vagus. 
30 
60% 
56 
45 
59 
57 
15 
49% 
Stimulus on vagus. 
58 
50+ 
59 
52+ 
1 
52% 
Stimulus off accelerators. 
1 
15 
48 
3 
47 
5 
45 
Stimulus off vagus. 
30 
52% 
These figures show that after the two nerves had been stimulated 
together for about twenty minutes, the heart was beating at a rate 
which remained nearly constant (534 to 54 beats in 15 seconds) for 
the next 13 minutes, i. e., till the stimulation of the vagus ceased. 
That this rate is a result of the effects produced upon the heart by 
the stimulation of the two nerves is indicated by the fact that as soon Reid Hunt 
177 
as the stimulus was removed from the vagus the heart rate increased 
from to 6(H beats in 15 seconds. Of course it may be objected 
that this was merely the return of the heart to its normal rate, which 
had been 61 before the nerves were stimulated, and the conclusion 
drawn that the accelerators had become completely exhausted and 
were no longer exerting any effect upon the heart. But the rate after 
the stimulation was but 51 in 15 seconds, and it is very probable that 
this number, rather than 61, represents the normal rate at this period 
of the stimulation. All doubt, however, as to whether the stimula- 
tion of the accelerators was still producing an effect upon the heart is 
at once removed by examining the figures immediately following. 
These show that when the vagus was again stimulated and the heart 
was beating at the rate of 52 beats in 15 seconds, taking the stimulus 
off the annulus caused the heart rate to fall to 45 in 15 seconds, which 
was the slowest rate reached during the experiment. 
This experiment shows that the heart can be kept beating for a con- 
siderable period of time at a rate not far from the normal, but one 
which is determined by the stimulation of the vagus and accelerators. 
This is the result which I think would be expected on the theory that 
the vagi are anabolic and the accelerators katabolic nerves, provided 
that the two nerves were stimulated to about equal degrees. What 
the result would be of stimulating the nerves for a long period with 
currents unequal in strength my experiments are not sufficiently 
numerous to decide, but they suggest the following: When the vagus 
effect is the stronger, the heart rate finally reached is one below the 
normal, but above that produced by stimulation of the vagus alone; 
on the other hand I have failed so far to see a case in which stimula- 
tion of the accelerators kept the heart beating above the normal rate 
for a very long period, though, as in the experiment quoted above, 
it might maintain the rate at the normal, notwithstanding a continu- 
ous stimulation of the vagus. 
Such results as the above, which my experiments so far indicate, 
might, I think, be easily explained on Gaskell’s theory, for we know 
that stimulation of the vagus will keep the heart slowed almost in- 
definitely, and if this be due to an anabolic action of this nerve, the 178 
Relation of Inhibitory to Accelerator Nerves of Heart 
weak stimulation of nerves causing katabolism, i. e., the accelerators, 
would be expected to destroy a part, but only a part, of the products 
of this anabolism, and the final effect would be that the heart rate 
would reach a level below the normal, but still above that caused by 
the stimulation of the vagus alone; and this seems to be what actually 
occurs. On the other hand it is difficult to see how katabolic nerves, 
however powerfully stimulated, could cause any prolonged increase 
of the heart rate above the normal, for the supply of the products of 
anabolism would soon be exhausted, even though the anabolic nerves 
were being stimulated at the same time; in other words, the katabolism 
cannot be greater than the anabolism for any great length of time. 
Hence the final result of a long-continued stimulation of the accelera- 
tors with a maximum stimulus combined with a weaker stimulation 
of the vagus would be the production of a heart rate about the normal, 
but which is still determined by the two stimulations. This is what 
seems to have actually occurred in the second experiment described 
above; that the stimulus applied to the accelerators was at least a 
maximal, and probably a super-maximal, stimulus is shown by the 
fact that a weaker current caused the same maximum acceleration. 
I desire to add, however, that these views are put forward only 
tentatively; subsequent experiments may show them to be incorrect. 
The chief object in introducing these experiments here at all is to 
show for what long periods the two nerves may be stimulated together 
without either overcoming the effect produced by the other. 
The experiments described in Part IV of this paper show that in 
whatever manner the problem of the relation of the vagus to the 
accelerators is approached, whether the accelerators are stimulated 
•during a stimulation of the vagus, or the vagus during a stimulation 
of the accelerators, or both are stimulated simultaneously, either for 
a short or for a longer period, the result is the same, viz., the effect 
upon the rate of the heart is determined entirely by the relative 
strength of the stimuli applied to the two nerves. If the stimuli are 
of approximately the same strength, as judged by the effect of stimu- 
lating the nerves separately, the rate of the heart is but slightly 
CONCLUSION. Reid Hunt 
179 
affected; if the stimulus applied to the vagus is the stronger, the heart 
is slowed; if it is weaker, the heart is accelerated. In all cases the 
result of stimulating the two nerves simultaneously is approximately 
the algebraic sum of the results of stimulating them separately; some- 
times the inhibitory effect slightly predominates, but not more fre- 
quently than does the accelerator effect. Moreover, the two nerves 
may be stimulated simultaneously for a considerable period of time 
without either completely overcoming the effect of the other. 
Thus as far as their effect upon the rate of the ventricular beat is 
concerned, the vagus and accelerator nerves seem to be purely antag- 
onistic; the statement that a minimal stimulation of the one can com- 
pletely overcome a maximal stimulation of the other is undoubtedly 
incorrect, and the hypotheses as to the mode of action of these nerves 
upon the heart, based upon this statement, lose their chief support. 
NOTE. 
Results very similar to those described in the above paper were 
obtained by Mr. Conant and myself in an experiment upon a crab.* 
One of the accelerator nerves of this animal was stimulated a number 
of times during the standstill produced by a long-continued stimula- 
tion of one of the inhibitory nerves; in each case the heart began 
to beat and continued beating during the stimulation of the accelera- 
tor, stopping completely again as soon as this stimulation was dis- 
continued. The accelerator alone was now stimulated and a marked 
acceleration obtained; while this stimulation continued the inhibitory 
nerve was stimulated, with the result that while the acceleration was 
diminished the heart rate was still about the normal. The stimulus 
was removed from the accelerator nerve, while that on the inhibitory 
remained; total inhibition resulted. 
It is interesting to note that in the crab the irritability of the inhi- 
bitory and accelerator nerves seems to be much more nearly equal 
than is the case in the mammal; in the above experiment a stimulus 
of sufficient strength just to cause total inhibition was sufficient to 
cause an almost maximal acceleration. 
* For a description of the cardiac nerves in the crab, see the article by 
Conant and Clark, The Journal of Experimental Medicine, i, p. 341, 1896.