ids should have no specially allotted destination, since every
part of the machine has to be maintained. But not so with the other
substances. The carbohydrates are distributed very unequally, and this
inequality of distribution seems to us in the highest degree
instructive.

Conveyed by the arterial blood in the form of glucose, these substances
are deposited, in the form of glycogen, in the different cells forming
the tissues. We know that one of the principal functions of the liver is
to maintain at a constant level the quantity of glucose held by the
blood, by means of the reserves of glycogen secreted by the hepatic
cells. Now, in this circulation of glucose and accumulation of glycogen,
it is easy to see that the effect is as if the whole effort of the
organism were directed towards providing with potential energy the
elements of both the muscular and the nervous tissues. The organism
proceeds differently in the two cases, but it arrives at the same
result. In the first case, it provides the muscle-cell with a large
reserve deposited in advance: the quantity of glycogen contained in the
muscles is, indeed, enormous in comparison with what is found in the
other tissues. In the nervous tissue, on the contrary, the reserve is
small (the nervous elements, whose function is merely to liberate the
potential energy stored in the muscle, never have to furnish much work
at one time); but the remarkable thing is that this reserve is restored
by the blood at the very moment that it is expended, so that the nerve
is instantly recharged with potential energy. Muscular tissue and
nervous tissue are, therefore, both privileged, the one in that it is
stocked with a large reserve of energy, the other in that it is always
served at the instant it is in need and to the exact extent of its
requirements.

More particularly, it is from the sensori-motor system that the call for
glycogen, the potential energy, comes, as if the rest of the organism
were simply there in order to transmit force to the nervous system and
to the muscles which the nerves control. True, when we think of the part
played by the nervous system (even the sensori-motor system) as
regulator of the organic life, it may well be asked whether, in this
exchange of good offices between it and the rest of the body, the
nervous system is indeed a master that the body serves. But we shall
already incline to this hypothesis when we consider, even in the static
state only,