344 
difference of contour between Figs. 1 and 2 represents | 
the effect of the arrival of the wave of excitation at the 
distal electrode @. The proof that this is so is as follows 
(see diagram, Fig. 3):—From the measurement of the 
polar ordinates of Fig. 1 we obtain by calculation the | 
curve P’, which represents the change which occurs in the | 
Fic. 2 —The same as Fig. 1 after cancelling the excitatory change at p. 
difference of potential between the surface of contact / 
and the rest of the surface of the muscle during the period 
of excitation.! We assume an identical curve b’ in the 
same relation to the contact d, differing from P’ only in 
the opposite sign of its ordinates, and relating to a period 
a little (in the case represented 15/1000 sec.) later than 
of Pp’ ; and by summing the synchronous ordinates of the 
two curves P’ and D’ algebraically, we obtain the curve s’, 
which expresses what must be the successive differences 
of potential between # and d@ when the effect of the change 
at d@ 7s not cancelled. If we deduce this curve by calcu- 
lation from Fig. 2, the two curves, ze. the deduced 
curve and the summation curve, ought to coincide. Their 
actual coincidence shows that the relation between the 
curves P’, D’ and Ss’ has been correctly understood ; it 
affords satisfactory proof that from P’ we can deduce Ss’, 
and consequently good reason for making the determin- 
ation of P’, ze. the monophasic variation, the aim of our 
experimental method. 
With reference to this method there are two points 
still to be adverted to. One is that it gives us the means 
of measuring with great exactitude the rate of propaga- 
tion of the “excitatory wave,” the progress of which 
from the seat of excitation has been already mentioned, 
and of proving that, although it varies according to the 
temperature and the vitality of the muscle, it is, under 
unchanging conditions, fairly constant. The other point 
relates to the mode of cancelling the effect of the wave 
of excitation at the distal electrode. The most effectual 
and simplest way of doing this is to apply a tight 
ligature across the path of propagation, the effect of 
which is to arrest the progress of the wave in its course 
from # tod. Another method is to devitalise the part 
of the muscle to which the distal electrode is applied by 
heat. The result in the two cases is the same as regards 
the electrical response to excitation. Fig. 1 is converted 
into Fig. 2. But as regards the electrical state of the 
muscle when at rest it is different—z.e. when the ligature 
is applied half-way between # and d the contacts 
remain equipotential, or nearly so; whereas in the other 
case the unexcited and unexcitable dead surface is found 
to be strongly negative to the other. 
We are now in a position to sum up what is to be 
learned from the first fundamental experiment. The 
most important result is that, both as regards the muscle 
when “at rest” and the change of state which is evoked | 
by excitation, the observed instrumental effect depends | 
exclusively on the state of the surfaces of contact, and 
consequently, when the distal contact is cancelled, on 
that of the proximal contact only. | 
Second Fundamental Experiment.—We have so far | 
1 The way in which the curve p’ is deduced is fully given in the paper 
quoted above in the Journal of Physiology, vol. xxiii. | 
NO. 1554, VOL. 60] 
NWATORE 
(See diagram on p. 343.) 
(AucusT 10, 1899 
only considered experimentally the effects of a single 
instantaneous excitation on muscle, causing it to give 
the mechanical effect known as a twitch. We have now 
to inquire what are the electrical concomitants of 
continuous contraction. This part of the subject has 
greater interest than the one we have been considering, 
inasmuch as it involves the question 
of the nature of ordinary voluntary 
muscular action, with reference to 
which there are reasons for holding 
that its continuity is apparent only. 
One of the chief of such reasons is to 
be found in the supposed resemblance 
of the sound of a muscle contracting 
normally to the musical sound of a 
muscle subjected to a rapid series of 
instantaneous stimuli. It is ordinarily 
stated that inasmuch as we can pro- 
duce continuous contraction by discon- 
tinuous stimulation (artificial tetanus), 
all continuous contraction is so pro- 
duced. Putting aside the question of muscle-sound, 
which does not here concern us, and confining ourselves 
to the electrical concomitants of continuous action, it 
can be shown that under certain conditions a continuous 
effect can be evoked by a single uninterrupted stimulus, 
and that in the nearest ap- 
proach we can get to natural 
contraction, the reflex spasm, 
there is no evidence of discon- 
tinuity 27 the sense in which 
this 7s usually understood. Let 
us first see what are the elec- 
trical concomitants of artificial 
tetanus. If the muscle is com- 
pletely tetanised, 7.2. subjected 
to a succession of stimuli at 
the rate of over 50 per second, 
the electrometer gives us a 
curve, of which the general 
form is shown in Fig. 4.. The 
muscle passes at once from 
the state of capacity for action 
into the state of action. This 
is indicated by the sudden 
manifestation of a difference 
of potential, which persists as 
long as its cause. 
When the rate of excitation 
is less frequent, the electro- 
meter curve gives evidence 
that the tetanus, whether still 
mechanically complete, or al- 
ready incomplete, is composed 
of a series of twitches, 7.e. 
of single monophasic effects. 
[Photographs were shown of 
the response in a sartorius, de- 
vitalised under the distal elec- 
trode, and excited by a series 
of instantaneous stimuli fol- 
lowing each other with a fre- 
eae of So) etal nee Ole ibs which they indicate and be- 
case, 20 per Sec. in the other. } tween the monophasic curves 
lie however, while still re- vp’ and p’ and the diphasic s’. 
taining the higher frequency, Th numbers below fe hors 
we subject the muscle to a of a second. 
series of short tetanising ex- 
citations, each lasting say for a tenth of a second or 
more, and succeeded by a rest of similar duration, we 
obtain a curve of alternate polarisation and depolarisation 
such as would represent short, but persisting, differences 
of potential, alternating with periods of indifference 
(Fig. 5). 
il 
Fic. 
relation between the photo- 
graphic curves and the curves 
3.—Diagram showing the 
of difference of potential 
