628 
NATURE 
[OcToBER 26, 1899 
Certainly we must allow for the unforeseen ; we must recognise 
the possibility that, perchance at no very distant date, we may 
receive the formal demonstration of fundamental differences be- 
tween electrical and nervous vibrations, and have to admit that 
the latter possess special characters which differentiate them 
from all known classes of vibrations. 
Vv. 
I now come to a different order of facts, on which I will speak 
more fully, for I have to deal with my own researches, some, 
indeed, as yet unpublished. These I carried on in collaboration 
with M. André Broca ; they are, I think, of a character likely 
to shed light on some of the conditions of the nerve-wave. True, 
they tell us nothing of the actual nature of nerve-vibration ; but 
they will allow us to deduce the form of the nerve-wave. 
Our experiments were made on the nerve-centres, not on the 
peripheral nerves ; as a matter of fact, we believe that the laws | 
which we have discovered for the one will apply to the other, 
and Charpentier’s recent and most ingenious researches confirm 
this assimilation. 
We must go back to the very definition of a vibration. We 
have seen that it is a movement of oscillation, an object is 
removed from a position of equilibrium and comes back to it | 
again. Such is a szmple oscillation ; in a complete wave, after 
returning to the position of equilibrium from the furthest point, 
it passes that position and only returns after a certain traverse 
in the opposite direction. 
If we call the first simple oscillation from the position of, 
equilibrium the Josztive phase, the second oscillation is regarded 
as the megative phase of the complete wave. Now the phe- 
nomenon is no simple one; the return to equilibrium is not 
Typed. 
Fic. 1. | 
| 
durable, and if no new condition intervene the vibration will 
continue. Were there no friction or resistance the vibration 
would persist indefinitely ; for there is no reason for the motion | 
to stop, and the pendulum, to take the very simplest case, | 
would never return to rest at its original position of stable 
equilibrium. To stop the vibration there must be some deadening 
or damping process. | 
Physicists have studied the modes of damping, and find that | 
they are divided into three types. | 
Type a is that of a pendulum, a vibrating string, or the waves | 
of liquid when a stone enters the water. A series of complete | 
waves follow with smaller and smaller oscillations, and the | 
vibration dies out by the gradual decrease of the waves— | 
secondary, tertiary, &c.—which followed the primary wave. 
This type of damping is, as we have said, due to the resistance | 
of the medium consuming part of the energy ; for, theoretically, 
a vibration once started would never stop. You are familiar 
with the fact that a pendulum continues to swing much longer | 
in vacuo than in the air, and I need not dwell further on this | 
point (Fig. 1). 
Type 8 shows a very different character in its damping. | 
After the pendulum has completed its first phase and passed | 
the point of equilibrium, it meets a certain obstacle to its return 
point ; it only swings back again very slowly thereto, and on 
reaching it it cannot pass beyond it. Indeed, from diverse 
theoretical considerations it may be proved that it never returns 
absolutely to the point of equilibrium; it approaches it in- 
definitely without ever reaching it; in short, ABA’ is an 
asymptotic curve of which Aa’ is the asymptote. Later on we | 
shall see what conclusions may be drawn from this as to the 
nature of the nerve-wave. Suffice it now to demonstrate the 
form of the wave with this type of damping. Practically, stable | 
equilibrium is reached sooner than by type a: indeed, this is | 
the type of damping used in the transmission of signals by sub- 
NO. 1565, VOL. 60] 
marine cables ; where it is necessary to prevent each signal from 
producing a whole series of swings of the galvanometer needle, 
and to obtain as rapidly as possible its return to equilibrium and 
rest (Fig. 2). 
Type 7 remains to be described: here the pendulum, after 
being moved from the point of equilibrium, returns only very 
slowly to that position ; this it does, for example, when hang- 
ing in a very dense medium. In this type of damping, as in B, 
there are no consecutive secondary and tertiary vibrations ; nay, 
more, the damping is here so complete that there is no negative 
phase, only a simple oscillation, This curve is also asymptotic, 
and the return never reaches the primitive state of equilibrium 
(Fig. 3). 
We see at once that the form of the wave is determined in 
each case by the type of its damping, and our experiments have 
B 
Fic. 2. 
enabled us to determine the character of the damping of the 
nerve-wave. We might have set type a aside @ przorz; it 
would have been unreasonable to suppose it. If to wave I 
succeeded waves 2, 3, 4, &c., a single stimulus would produce 
a whole series of responses ; now this is not the case with the 
nerve. Hence the damping must be on the type of 8 or of y. 
But obvious as these considerations are when once stated, we 
did not reach them @ frtor¢; it required actual experience to 
enlighten us ; so true is it that in science, at least in physio- 
logical science, experiment is more fertile than dialectic. 
VI. 
The following were the methods by which we determined 
the form of the nerve-wave. I will not describe our research in 
order of time ; I shall only select some of the simplest, the most 
demonstrative, experiments. We know that but rarely are the 
earlier experiments one or the other; they are complex and 
Type ry. 
A 
Fic. 3. 
slow, and it is only by degrees that one learns how to simplify 
them and make them direct. 
A dog is anzesthetised by the injection of a sufficient dose of 
chloralose into the veins (o°r gramme to the kilo. of live weight), 
and electrodes are applied to the surface of its head. We can 
now observe the effects of an electric stimulus on the cerebral 
cortex under excellent conditions. The electrodes can be fixed 
immovably, so that the same part of the cortex is always 
stimulated ; and the effects of the stimulus are always localised 
in the same muscles. If we repeat the same electric stimulus, 
supplied by a secondary current from accumulators, always of 
the same suitable intensity, we find that each successive electric 
shock, repeated at intervals of one second, calls forth a regular 
and equal muscular contraction in response. This regularity is 
complete, and if the conditions of circulation and respiration are 
kept satisfactory for one, two, or even three hours, we have a 
