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the organic. All the progress made, during the present century, it physi-
ological anatomy, has contributed to the perfecting of this theory of
intermittence. Rationality understood, it applies immediately to a very
extensive and important class of animal phenomena; that is, to those
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which belong to the different degrees of sleep. The state of sleep thus
consists of the simultaneous suspension, for a certain time, of the prin-
cipal actions of irritability and sensibility. It is as complete as the orga-
nization of the superior animals admits when it suspends all motions
and sensations but such as are indispensable to the organic life,—their
activity being also remarkably diminished. The phenomenon admits of
great variety of degrees, from simple somnolence to the torpor of
hybernating animals. But this theory of sleep, so well instituted by Bichat,
is still merely initiated, and presents many fundamental difficulties, when
we consider the chief modifications of such a state, even the organic
conditions of which are very imperfectly known, except the stagnation
of the venous blood in the brain, which appears to be generally an indis-
pensable preliminary to all extended and durable lethargy. If is easy to
conceive how the prolonged activity of the animal functions in a waking
state may, by the law of intermittence, occasion a proportional suspen-
sion but it is not so, easy to see why the suspension should be total when
the activity has been only partial. Yet we see how profound is the sleep,
intellectual and muscular, induced by fatigue of the muscles alone in
men who, while awake, have often very little exercise to their sensibil-
ity, interior, or even exterior. We know still less of incomplete sleep;
especially when only a part of the intellectual or affective turbans, or of
the locomotive apparatus is torpid, whence arise dreams and various
kinds of somnambulism. Yet such a state has certainly its own general
laws, as well as the waking state. Some experiments, not duly attended
to perhaps justify the idea that, in animals, in which the cerebral life is
much less varied, the nature of dreams becomes, to a certain point, sus-
ceptible of being directed at the pleasure of the observer, by the aid of
external impressions produced, during sleep, upon the senses whose
action is involuntary; and especially smell. And in the case of Man,
there is no thoughtful physician who, in certain diseases, does not take
into the account the habitual character of the patient’s dreams, in order
to perfect the diagnosis of maladies in which the nervous system is espe-
cially implicated: and this supposes that the state is subject to determi-
nate laws, though they may be unknown. But, however imperfect the
theory of sleep may still be, in these essential respects, it is fairly consti-
tuted upon a positive basis of its own; for, looked at as a whole, it is
explained, according to the scientific acceptation of the term, by its
radical identity with the phenomena of partial repose offered by all the
elementary acts of the animal life. When the theory of intermittence is
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perfected, we shall, I imagine, adopt Gall’s view of connecting it with
the sympathy which characterizes all the organs of animal life, by re-
garding the two parts of the symmetrical apparatus as alternately active
and passive, so that their function is never simultaneous: and this, as
much in regard to the external senses as the intellectual organs. All this,
however, deserves a fresh and thorough investigation.
The theory of Habit is a sort of necessary appendix to that of inter-
mittence; and, like it, due to Bichat. A continuous phenomenon would
be, in fact, capable of persistence, in virtue of the law of inertia: but
intermittent phenomena alone can give rise to habits properly so called:
that is, can tend to reproduce themselves spontaneously through the
influence of a preliminary repetition, sufficiently prolonged at suitable
intervals. The importance of this animal property is now universally
acknowledged among able inquirers, who see in it one of the chief bases
of the gradual perfectibility cf animals, and especially of Man. Through
this it is that vital phenomena may, in some sort, participate in the admi-
rable regularity of those of the inorganic world, by becoming, like them,
periodical, notwithstanding their greater complexity. Hence also results
the transformations,—optional up to a certain point of inveteracy of
habit, and inevitable beyond that point,—of voluntary acts into invol-
untary tendencies. But the study of habit is no further advanced than
that of intermittence, in regard to its analysis: for we have paid more
attention hitherto to the influence of habits once contracted than to their
origin, with regard to which scarcely any scientific doctrine exists. What
is letdown lies in the department of natural history, and not in that of
biology. Perhaps it may be found, in the course of scientific study, that
we have been too hasty in calling this an animal property, though the
animal structure may be more susceptible of it. In fact, there is no doubt
that inorganic apparatus admits of a more easy reproduction of the same
acts after a sufficient regular and prolonged reiteration, as I had occa-
sion to observe in regard to the phenomenon of sound: and this is essen-
tially the character of animal habit. According to this view, which I
commend to the attention of biologists, and which, if true, would consti-
tute the most general point of view on this subject, the law of habit may
be scientifically attached to the law of inertia, as geometers understand
it in the positive theory of motion and equilibrium.
In examining the phenomena common to irritability and sensibility
under the aspect of their activity, physiologists have to examine the two
extreme terms,—exaggerated action, and insufficient action. in order to
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determine the intermediate normal degree for the study of intermediate
cases can never be successfully undertaken till the extreme cases which
comprehend then; have been first examined.
The need of exercising the faculties is certain the most general and
important of all those that belong to the animal life: we may even say
that it comprehends them all, if we exclude what relates merely to the
organic life. The existence of an animal organ is enough to awaken the
need immediately. We shall see, in the next volume, that this consider-
ation is one of the chief bases that social physics derives from individual
physiology. Unhappily this study is still very imperfect with regard to
most of the animal functions, and to all the three degrees of their activ-
ity. To it we must refer the analysis of all the varied phenomena of
pleasure and pain, physical and moral. The case of defect has been even
less studied than that of excess; and yet its scientific examination is
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