| uly 31, 1873] 
THE ORIGIN OF NERVE FORCE 
iP 
pe any one taking a general view of the present posi- 
a tion of physiology, there are few things more striking 
than the deficiency of our knowledge respecting the source 
of the current which traverses the nervous system, and is 
brought into play through the instrumentality of its 
various parts. That the current itself is electricity in some 
form or another, is almost universally acknowledged, but 
in what part of the body it originates, or from what store 
of energy it is derived, is more than most have attempted 
to answer. The question is made more difficult than it 
would otherwise be, from the fact that in all those animals 
which exhibit external electrical phenomena to any extent, 
such as the Torpedo and Gymnotus, there are large and 
elaborate special organs for the development of the 
shocks they produce, but no similar mechanicism, 
and nothing approaching to it, can be detected in man or 
other animals, whereby an electrical current or charge 
might originate. The brain and the various ganglia are 
often compared to the batteries of a system of electric 
telegraph, but how they would act if they were such, it is 
almost impossible to explain. 
Direct evidence, therefore, failing to give a satisfactory 
solution of the problem as to whence nerve force 
Originates, it is necessary to appeal to the indirect in 
endeavouring to obtain an answer. The hypothesis of 
“the survival of the fittest” evidently presupposes that 
after the struggle for existence has lasted a certain time, 
the individuals which remain, economise to the utmost all 
the forces at their disposal, because the more perfect use 
that a living being can make of the limited forces at its 
command, the easier will it be for it to continue to live. 
The Rev. Samuel Haughton from the resulting very 
strongly marked economy of the animal mechanicism, 
has deduced the principle termed by him that of “least 
action in nature.” The generalness of this principle makes 
it necessary, if there is evidence of the existence of any 
store of energy in the living body apparently unemployed, 
to endeavour to find whether its effects have not been 
overlooked, or included with those of some other force ; 
and if, at the same time, a force is at work whose origin is 
unknown, to try and prove whether the two are in any way 
related to one another. As shown above, there is a force 
which is in continuous action, with an unexplained origin ; 
the question then resolves itself into whether there is a 
source of energy in-the living body, whose effects have 
not been explained, and if so, can it on any known or 
probable grounds, be considered competent to give rise to 
the nerve current? An endeavour will now be made to 
show that both parts of the question may be answered 
in the affirmative; in other words, that there is an 
available source of energy, as yet unrecognised, of 
which the function is therefore not yet explained, and 
which is quite capable of giving rise to the nerve 
current. 
This physiologically new source of energy is she 
differences of temperature between the interior and 
surface of the living body. Those who are unac- 
quainted with the principles of the modern doctrines 
of thermo-dynamics, will readily perceive that a difference 
of temperature in two bodies is a source of power, when 
they consider that a low-pressure steam engine depends, 
for its power of doing work, on the difference of tempera- 
ture between its boiler and condenser ; and that a current 
may be maintained through a copper wire, if it is connected 
with a thermo-electric battery of which the two ends are 
kept at different temperatures. In what are termed hot- 
blooded animals, that is, in mammals and birds, the 
difference of temperature between the surface and the in- 
terior is considerable under all natural circumstances, and 
in them there is a regulating action of the skin, by which 
they maintain a uniform internal temperature, always 
hotter than the surface, whatever that of the external 
~ 
Ss NATURE 
265 
medium may be. In the sluggish so-called cold-blooded 
animals, the temperature of the interior of the body is 
but slightly different from that of the air or water in which 
they live ; that it must be higher is evident from the fact 
that destruction of tissue is continually going on in their 
bodies, which is always necessarily attended with the 
evolution of heat. 
Such being the case, it is evident that in the difference 
of temperature between the surface and the interior of 
the living body there is an available source of energy, 
which is almost certainly employed advantageously 
throughout the whole animal kingdom; and what is 
more, it may reasonably be supposed to be that which 
gives rise to the electrical nerve current, as only one 
assumption is involved, and that not an improbable one, 
it being that a thermo-electric current is capable of being 
generated between soft tissues of different composition or 
structure. Physicists will be able to decide this question 
experimentally, and if they do so, they will do a service 
to physiology. 
For the distribution of a current so generated, the con- 
struction of the nervous system is perfectly suited. Two 
sets of conductors are necessary, the one to carry the 
currents from the skin to the central organ, which 
arranges the direction that they must take, and the other 
to send them on to their destination ; these are to be 
found in the afferent and efferent nerves. As in the 
telegraph system, no return conductor is necessary ; for 
as the ends of the wires are put into connection with the 
earth, by which they are able to communicate, so the 
terminations of the nerves in the skin, muscle-cor- 
puscles and otherwise where they lose their insulated 
coverings, place the extremities of the afferent and efferent 
nerves in communication through the intervention of the 
mass of body tissue. The brain and minor ganglia would 
then act like greater and lesser offices for the reception 
and transmission of currents in the required directions, 
being in fact the commutators of the system, 
There are several of the most important phenomena 
exhibited by the nervous system which are very satisfac- 
torily explained on the above hypothesis. For instance, 
in cold weather the impulse to action is much more 
powerfully felt, than in summer when the air is hot, and 
therefore the temperature of the surface is higher. It is 
well known that it is impossible to remain for more than 
a very short time in a hot water-bath, of which the tem- 
perature is as high as, or a little higher than, that of the 
body, on account of the faintness which is sure to come 
on, and this may be reasonably supposed to be the result 
of the cessation of the nerve current, which is consequent 
on the temperature of the surface of the body becoming 
the same as that of the interior. This faintness is imme- 
diately recovered from by the application of a cold douche. 
When great muscular exertion has to be sustained, as in 
running or rowing, it is always necessary to have the 
clothes very thin, and it is felt during the time that it is 
necessary for the continuance of the effort, that the sur- 
face of the body must be kept cool. 
As the termination of the nerves in the skin must 
correspond, on this hypothesis, with the cooled end of a 
thermo-electric battery, therefore the brain, which is very 
abundantly supplied with blood, and is the part of the 
body to which most of the nerves are directed, must 
be compared with the heated end; and as it is by the 
conversion of heat into electric current that the nerve 
force is developed, it is evident that heat must, to a certain 
extent, disappear as such in the brain, and that that organ 
must consequently be colder than the blood which enters 
it. This is exactly what Dr. John Davy observed in the 
case of the rabbits he experimented on, and his results 
have not been shown to be incorrect. 
A paper on this subject by the present writer appeared 
in the June number of the Fournal of Anatomy and 
Physiology. A, H. GArropD 
