Chapter I — GENERAL PRINCIPLES OF EXPRESSION

The three chief principles stated—The first principle—Serviceable
actions become habitual in association with certain states of the mind,
and are performed whether or not of service in each particular case—The
force of habit—Inheritance—Associated habitual movements in
man—Reflex actions—Passage of habits into reflex actions—Associated
habitual movements in the lower animals—Concluding remarks.

I will begin by giving the three Principles, which appear to me to account
for most of the expressions and gestures involuntarily used by man and the
lower animals, under the influence of various emotions and sensations.[101]
I arrived, however, at these three Principles only at the close of my
observations. They will be discussed in the present and two following
chapters in a general manner. Facts observed both with man and the lower
animals will here be made use of; but the latter facts are preferable, as
less likely to deceive us. In the fourth and fifth chapters, I will
describe the special expressions of some of the lower animals; and in the
succeeding chapters those of man. Everyone will thus be able to judge for
himself, how far my three principles throw light on the theory of the
subject. It appears to me that so many expressions are thus explained in a
fairly satisfactory manner, that probably all will hereafter be found to
come under the same or closely analogous heads. I need hardly premise that
movements or changes in any part of the body,—as the wagging of a
dog’s tail, the drawing back of a horse’s ears, the shrugging of a man’s
shoulders, or the dilatation of the capillary vessels of the skin,—may
all equally well serve for expression. The three Principles are as
follows.

I. The principle of serviceable associated Habits.—Certain
complex actions are of direct or indirect service under certain states of
the mind, in order to relieve or gratify certain sensations, desires,
&c.; and whenever the same state of mind is induced, however feebly,
there is a tendency through the force of habit and association for the
same movements to be performed, though they may not then be of the least
use. Some actions ordinarily associated through habit with certain states
of the mind may be partially repressed through the will, and in such cases
the muscles which are least under the separate control of the will are the
most liable still to act, causing movements which we recognize as
expressive. In certain other cases the checking of one habitual movement
requires other slight movements; and these are likewise expressive.

II. The principle of Antithesis.—Certain states of the mind
lead to certain habitual actions, which are of service, as under our first
principle. Now when a directly opposite state of mind is induced, there is
a strong and involuntary tendency to the performance of movements of a
directly opposite nature, though these are of no use; and such movements
are in some cases highly expressive.

III. The principle of actions due to the constitution of the Nervous
System, independently from the first of the Will, and independently to a
certain extent of Habit.—When the sensorium is strongly excited,
nerve-force is generated in excess, and is transmitted in certain definite
directions, depending on the connection of the nerve-cells, and partly on
habit: or the supply of nerve-force may, as it appears, be interrupted.
Effects are thus produced which we recognize as expressive. This third
principle may, for the sake of brevity, be called that of the direct
action of the nervous system.

With respect to our first Principle, it is notorious how powerful
is the force of habit. The most complex and difficult movements can in
time be performed without the least effort or consciousness. It is not
positively known how it comes that habit is so efficient in facilitating
complex movements; but physiologists admit[102] “that the conducting
power of the nervous fibres increases with the frequency of their
excitement.” This applies to the nerves of motion and sensation, as well
as to those connected with the act of thinking. That some physical change
is produced in the nerve-cells or nerves which are habitually used can
hardly be doubted, for otherwise it is impossible to understand how the
tendency to certain acquired movements is inherited. That they are
inherited we see with horses in certain transmitted paces, such as
cantering and ambling, which are not natural to them,—in the
pointing of young pointers and the setting of young setters—in the
peculiar manner of flight of certain breeds of the pigeon, &c. We have
analogous cases with mankind in the inheritance of tricks or unusual
gestures, to which we shall presently recur. To those who admit the
gradual evolution of species, a most striking instance of the perfection
with which the most difficult consensual movements can be transmitted, is
afforded by the humming-bird Sphinx-moth (Macroglossa); for this
moth, shortly after its emergence from the cocoon, as shown by the bloom
on its unruffled scales, may be seen poised stationary in the air, with
its long hair-like proboscis uncurled and inserted into the minute
orifices of flowers; and no one, I believe, has ever seen this moth
learning to perform its difficult task, which requires such unerring aim.

When there exists an inherited or instinctive tendency to the performance
of an action, or an inherited taste for certain kinds of food, some degree
of habit in the individual is often or generally requisite. We find this
in the paces of the horse, and to a certain extent in the pointing of
dogs; although some young dogs point excellently the first time they are
taken out, yet they often associate the proper inherited attitude with a
wrong odour, and even with eyesight. I have heard it asserted that if a
calf be allowed to suck its mother only once, it is much more difficult
afterwards to rear it by hand.[103] Caterpillars which
have been fed on the leaves of one kind of tree, have been known to perish
from hunger rather than to eat the leaves of another tree, although this
afforded them their proper food, under a state of nature;[104]
and so it is in many other cases.

The power of Association is admitted by everyone. Mr. Bain remarks, that
“actions, sensations and states of feeling, occurring together or in close
succession, tend to grow together, or cohere, in such a way that when any
one of them is afterwards presented to the mind, the others are apt to be
brought up in idea.”[105] It is so important for our purpose fully to
recognize that actions readily become associated with other actions and
with various states of the mind, that I will give a good many instances,
in the first place relating to man, and afterwards to the lower animals.
Some of the instances are of a very trifling nature, but they are as good
for our purpose as more important habits. It is known to everyone how
difficult, or even impossible it is, without repeated trials, to move the
limbs in certain opposed directions which have never been practised.
Analogous cases occur with sensations, as in the common experiment of
rolling a marble beneath the tips of two crossed fingers, when it feels
exactly like two marbles. Everyone protects himself when falling to the
ground by extending his arms, and as Professor Alison has remarked, few
can resist acting thus, when voluntarily falling on a soft bed. A man when
going out of doors puts on his gloves quite unconsciously; and this may
seem an extremely simple operation, but he who has taught a child to put
on gloves, knows that this is by no means the case.

When our minds are much affected, so are the movements of our bodies; but
here another principle besides habit, namely the undirected overflow of
nerve-force, partially comes into play. Norfolk, in speaking of Cardinal
Wolsey, says—

“Some strange commotion
Is in his brain; he bites his lip and starts;
Stops on a sudden, looks upon the ground,
Then, lays his finger on his temple: straight,
Springs out into fast gait; then, stops again,
Strikes his breast hard; and anon, he casts
His eye against the moon: in most strange postures
We have seen him set himself.”—Hen. VIII., act iii, sc. 2.

A vulgar man often scratches his head when perplexed in mind; and I
believe that he acts thus from habit, as if he experienced a slightly
uncomfortable bodily sensation, namely, the itching of his head, to which
he is particularly liable, and which he thus relieves. Another man rubs
his eyes when perplexed, or gives a little cough when embarrassed, acting
in either case as if he felt a slightly uncomfortable sensation in his
eyes or windpipe.[106]

From the continued use of the eyes, these organs are especially liable to
be acted on through association under various states of the mind, although
there is manifestly nothing to be seen. A man, as Gratiolet remarks, who
vehemently rejects a proposition, will almost certainly shut his eyes or
turn away his face; but if he accepts the proposition, he will nod his
head in affirmation and open his eyes widely. The man acts in this latter
case as if he clearly saw the thing, and in the former case as if he did
not or would not see it. I have noticed that persons in describing a
horrid sight often shut their eyes momentarily and firmly, or shake their
heads, as if not to see or to drive away something disagreeable; and I
have caught myself, when thinking in the dark of a horrid spectacle,
closing my eyes firmly. In looking suddenly at any object, or in looking
all around, everyone raises his eyebrows, so that the eyes may be quickly
and widely opened; and Duchenne remarks that[107] a person in trying
to remember something often raises his eyebrows, as if to see it. A Hindoo
gentleman made exactly the same remark to Mr. Erskine in regard to his
countrymen. I noticed a young lady earnestly trying to recollect a
painter’s name, and she first looked to one corner of the ceiling and then
to the opposite corner, arching the one eyebrow on that side; although, of
course, there was nothing to be seen there.

In most of the foregoing cases, we can understand how the associated movements
were acquired through habit; but with some individuals, certain strange
gestures or tricks have arisen in association with certain states of the mind,
owing to wholly inexplicable causes, and are undoubtedly inherited. I have
elsewhere given one instance from my own observation of an extraordinary and
complex gesture, associated with pleasurable feelings, which was transmitted
from a father to his daughter, as well as some other analogous facts.[108]
Another curious instance of an odd inherited movement, associated with the wish
to obtain an object, will be given in the course of this volume.

There are other actions which are commonly performed under certain
circumstances, independently of habit, and which seem to be due to
imitation or some sort of sympathy. Thus persons cutting anything with a
pair of scissors may be seen to move their jaws simultaneously with the
blades of the scissors. Children learning to write often twist about their
tongues as their fingers move, in a ridiculous fashion. When a public
singer suddenly becomes a little hoarse, many of those present may be
heard, as I have been assured by a gentleman on whom I can rely, to clear
their throats; but here habit probably comes into play, as we clear our
own throats under similar circumstances. I have also been told that at
leaping matches, as the performer makes his spring, many of the
spectators, generally men and boys, move their feet; but here again habit
probably comes into play, for it is very doubtful whether women would thus
act.

Reflex actions—Reflex actions, in the strict sense of the
term, are due to the excitement of a peripheral nerve, which transmits its
influence to certain nerve-cells, and these in their turn excite certain
muscles or glands into action; and all this may take place without any
sensation or consciousness on our part, though often thus accompanied. As
many reflex actions are highly expressive, the subject must here be
noticed at some little length. We shall also see that some of them
graduate into, and can hardly be distinguished from actions which have
arisen through habit?[109] Coughing and sneezing are familiar instances of
reflex actions. With infants the first act of respiration is often a
sneeze, although this requires the co-ordinated movement of numerous
muscles. Respiration is partly voluntary, but mainly reflex, and is
performed in the most natural and best manner without the interference of
the will. A vast number of complex movements are reflex. As good an
instance as can be given is the often-quoted one of a decapitated frog,
which cannot of course feel, and cannot consciously perform, any movement.
Yet if a drop of acid be placed on the lower surface of the thigh of a
frog in this state, it will rub off the drop with the upper surface of the
foot of the same leg. If this foot be cut off, it cannot thus act. “After
some fruitless efforts, therefore, it gives up trying in that way, seems
restless, as though, says Pflüger, it was seeking some other way, and at
last it makes use of the foot of the other leg and succeeds in rubbing off
the acid. Notably we have here not merely contractions of muscles, but
combined and harmonized contractions in due sequence for a special
purpose. These are actions that have all the appearance of being guided by
intelligence and instigated by will in an animal, the recognized organ of
whose intelligence and will has been removed.”[110]

We see the difference between reflex and voluntary movements in very young
children not being able to perform, as I am informed by Sir Henry Holland,
certain acts somewhat analogous to those of sneezing and coughing, namely,
in their not being able to blow their noses (i.e. to compress the nose
and blow violently through the passage), and in their not being able to
clear their throats of phlegm. They have to learn to perform these acts,
yet they are performed by us, when a little older, almost as easily as
reflex actions. Sneezing and coughing, however, can be controlled by the
will only partially or not at all; whilst the clearing the throat and
blowing the nose are completely under our command.

When we are conscious of the presence of an irritating particle in our
nostrils or windpipe—that is, when the same sensory nerve-cells are
excited, as in the case of sneezing and coughing—we can voluntarily
expel the particle by forcibly driving air through these passages; but we
cannot do this with nearly the same force, rapidity, and precision, as by
a reflex action. In this latter case the sensory nerve-cells apparently
excite the motor nerve-cells without any waste of power by first
communicating with the cerebral hemispheres—the seat of our
consciousness and volition. In all cases there seems to exist a profound
antagonism between the same movements, as directed by the will and by a
reflex stimulant, in the force with which they are performed and in the
facility with which they are excited. As Claude Bernard asserts,
“L’influence du cerveau tend donc à entraver les mouvements réflexes, à
limiter leur force et leur étendue.”[111]

The conscious wish to perform a reflex action sometimes stops or
interrupts its performance, though the proper sensory nerves may be
stimulated. For instance, many years ago I laid a small wager with a dozen
young men that they would not sneeze if they took snuff, although they all
declared that they invariably did so; accordingly they all took a pinch,
but from wishing much to succeed, not one sneezed, though their eyes
watered, and all, without exception, had to pay me the wager. Sir H.
Holland remarks[112] that attention paid to the act of
swallowing interferes with the proper movements; from which it probably
follows, at least in part, that some persons find it so difficult to
swallow a pill.

Another familiar instance of a reflex action is the involuntary closing of
the eyelids when the surface of the eye is touched. A similar winking
movement is caused when a blow is directed towards the face; but this is
an habitual and not a strictly reflex action, as the stimulus is conveyed
through the mind and not by the excitement of a peripheral nerve. The
whole body and head are generally at the same time drawn suddenly
backwards. These latter movements, however, can be prevented, if the
danger does not appear to the imagination imminent; but our reason telling
us that there is no danger does not suffice. I may mention a trifling
fact, illustrating this point, and which at the time amused me. I put my
face close to the thick glass-plate in front of a puff-adder in the
Zoological Gardens, with the firm determination of not starting back if
the snake struck at me; but, as soon as the blow was struck, my resolution
went for nothing, and I jumped a yard or two backwards with astonishing
rapidity. My will and reason were powerless against the imagination of a
danger which had never been experienced.

The violence of a start seems to depend partly on the vividness of the
imagination, and partly on the condition, either habitual or temporary, of
the nervous system. He who will attend to the starting of his horse, when
tired and fresh, will perceive how perfect is the gradation from a mere
glance at some unexpected object, with a momentary doubt whether it is
dangerous, to a jump so rapid and violent, that the animal probably could
not voluntarily whirl round in so rapid a manner. The nervous system of a
fresh and highly-fed horse sends its order to the motory system so
quickly, that no time is allowed for him to consider whether or not the
danger is real. After one violent start, when he is excited and the blood
flows freely through his brain, he is very apt to start again; and so it
is, as I have noticed, with young infants.

A start from a sudden noise, when the stimulus is conveyed through the
auditory nerves, is always accompanied in grown-up persons by the winking
of the eyelids.[113] I observed, however, that though my infants
started at sudden sounds, when under a fortnight old, they certainly did
not always wink their eyes, and I believe never did so. The start of an
older infant apparently represents a vague catching hold of something to
prevent falling. I shook a pasteboard box close before the eyes of one of
my infants, when 114 days old, and it did not in the least wink; but when
I put a few comfits into the box, holding it in the same position as
before, and rattled them, the child blinked its eyes violently every time,
and started a little. It was obviously impossible that a carefully-guarded
infant could have learnt by experience that a rattling sound near its eyes
indicated danger to them. But such experience will have been slowly gained
at a later age during a long series of generations; and from what we know
of inheritance, there is nothing improbable in the transmission of a habit
to the offspring at an earlier age than that at which it was first
acquired by the parents.

From the foregoing remarks it seems probable that some actions, which were
at first performed consciously, have become through habit and association
converted into reflex actions, and are now so firmly fixed and inherited,
that they are performed, even when not of the least use,[114]
as often as the same causes arise, which originally excited them in us
through the volition. In such cases the sensory nerve-cells excite the
motor cells, without first communicating with those cells on which our
consciousness and volition depend. It is probable that sneezing and
coughing were originally acquired by the habit of expelling, as violently
as possible, any irritating particle from the sensitive air-passages. As
far as time is concerned, there has been more than enough for these habits
to have become innate or converted into reflex actions; for they are
common to most or all of the higher quadrupeds, and must therefore have
been first acquired at a very remote period. Why the act of clearing the
throat is not a reflex action, and has to be learnt by our children, I
cannot pretend to say; but we can see why blowing the nose on a
handkerchief has to be learnt.

It is scarcely credible that the movements of a headless frog, when it
wipes off a drop of acid or other object from its thigh, and which
movements are so well coordinated for a special purpose, were not at first
performed voluntarily, being afterwards rendered easy through
long-continued habit so as at last to be performed unconsciously, or
independently of the cerebral hemispheres.

So again it appears probable that starting was originally acquired by the
habit of jumping away as quickly as possible from danger, whenever any of
our senses gave us warning. Starting, as we have seen, is accompanied by
the blinking of the eyelids so as to protect the eyes, the most tender and
sensitive organs of the body; and it is, I believe, always accompanied by
a sudden and forcible inspiration, which is the natural preparation for
any violent effort. But when a man or horse starts, his heart beats wildly
against his ribs, and here it may be truly said we have an organ which has
never been under the control of the will, partaking in the general reflex
movements of the body. To this point, however, I shall return in a future
chapter.

The contraction of the iris, when the retina is stimulated by a bright
light, is another instance of a movement, which it appears cannot possibly
have been at first voluntarily performed and then fixed by habit; for the
iris is not known to be under the conscious control of the will in any
animal. In such cases some explanation, quite distinct from habit, will
have to be discovered. The radiation of nerve-force from strongly-excited
nerve-cells to other connected cells, as in the case of a bright light on
the retina causing a sneeze, may perhaps aid us in understanding how some
reflex actions originated. A radiation of nerve-force of this kind, if it
caused a movement tending to lessen the primary irritation, as in the case
of the contraction of the iris preventing too much light from falling on
the retina, might afterwards have been taken advantage of and modified for
this special purpose.

It further deserves notice that reflex actions are in all probability
liable to slight variations, as are all corporeal structures and
instincts; and any variations which were beneficial and of sufficient
importance, would tend to be preserved and inherited. Thus reflex actions,
when once gained for one purpose, might afterwards be modified
independently of the will or habit, so as to serve for some distinct
purpose. Such cases would be parallel with those which, as we have every
reason to believe, have occurred with many instincts; for although some
instincts have been developed simply through long-continued and inherited
habit, other highly complex ones have been developed through the
preservation of variations of pre-existing instincts—that is,
through natural selection.

I have discussed at some little length, though as I am well aware, in a
very imperfect manner, the acquirement of reflex actions, because they are
often brought into play in connection with movements expressive of our
emotions; and it was necessary to show that at least some of them might
have been first acquired through the will in order to satisfy a desire, or
to relieve a disagreeable sensation.

Associated habitual movements in the lower animals.—I have
already given in the case of Man several instances of movements associated
with various states of the mind or body, which are now purposeless, but
which were originally of use, and are still of use under certain
circumstances. As this subject is very important for us, I will here give
a considerable number of analogous facts, with reference to animals;
although many of them are of a very trifling nature. My object is to show
that certain movements were originally performed for a definite end, and
that, under nearly the same circumstances, they are still pertinaciously
performed through habit when not of the least use. That the tendency in
most of the following cases is inherited, we may infer from such actions
being performed in the same manner by all the individuals, young and old,
of the same species. We shall also see that they are excited by the most
diversified, often circuitous, and sometimes mistaken associations.

Dogs, when they wish to go to sleep on a carpet or other hard surface,
generally turn round and round and scratch the ground with their fore-paws
in a senseless manner, as if they intended to trample down the grass and
scoop out a hollow, as no doubt their wild parents did, when they lived on
open grassy plains or in the woods. Jackals, fennecs, and other allied
animals in the Zoological Gardens, treat their straw in this manner; but
it is a rather odd circumstance that the keepers, after observing for some
months, have never seen the wolves thus behave. A semi-idiotic dog—and
an animal in this condition would be particularly liable to follow a
senseless habit—was observed by a friend to turn completely round on
a carpet thirteen times before going to sleep.

Many carnivorous animals, as they crawl towards their prey and prepare to
rush or spring on it, lower their heads and crouch, partly, as it would
appear, to hide themselves, and partly to get ready for their rush; and
this habit in an exaggerated form has become hereditary in our pointers
and setters. Now I have noticed scores of times that when two strange dogs
meet on an open road, the one which first sees the other, though at the
distance of one or two hundred yards, after the first glance always lowers
its bead, generally crouches a little, or even lies down; that is, he
takes the proper attitude for concealing himself and for making a rush or
spring although the road is quite open and the distance great. Again, dogs
of all kinds when intently watching and slowly approaching their prey,
frequently keep one of their fore-legs doubled up for a long time, ready
for the next cautious step; and this is eminently characteristic of the
pointer. But from habit they behave in exactly the same manner whenever
their attention is aroused (fig. 4). I have seen a dog at the foot of a
high wall, listening attentively to a sound on the opposite side, with one
leg doubled up; and in this case there could have been no intention of
making a cautious approach.

{illust. caption = for making a rush or FIG. 4.—Small dog watching a
cat on a table. From a photograph taken by Mr. Rejlander.}

Dogs after voiding their excrement often make with all four feet a few
scratches backwards, even on a bare stone pavement, as if for the purpose
of covering up their excrement with earth, in nearly the same manner as do
cats. Wolves and jackals behave in the Zoological Gardens in exactly the
same manner, yet, as I am assured by the keepers, neither wolves, jackals,
nor foxes, when they have the means of doing so, ever cover up their
excrement, any more than do dogs. All these animals, however, bury
superfluous food. Hence, if we rightly understand the meaning of the above
cat-like habit, of which there can be little doubt, we have a purposeless
remnant of an habitual movement, which was originally followed by some
remote progenitor of the dog-genus for a definite purpose, and which has
been retained for a prodigious length of time.

Dogs and jackals[115] take much pleasure in rolling and rubbing
their necks and backs on carrion. The odour seems delightful to them,
though dogs at least do not eat carrion. Mr. Bartlett has observed wolves
for me, and has given them carrion, but has never seen them roll on it. I
have heard it remarked, and I believe it to be true, that the larger dogs,
which are probably descended from wolves, do not so often roll in carrion
as do smaller dogs, which are probably descended from jackals. When a
piece of brown biscuit is offered to a terrier of mine and she is not
hungry (and I have heard of similar instances), she first tosses it about
and worries it, as if it were a rat or other prey; she then repeatedly
rolls on it precisely as if it were a piece of carrion, and at last eats
it. It would appear that an imaginary relish has to be given to the
distasteful morsel; and to effect this the dog acts in his habitual
manner, as if the biscuit was a live animal or smelt like carrion, though
he knows better than we do that this is not the case. I have seen this
same terrier act in the same manner after killing a little bird or mouse.

Dogs scratch themselves by a rapid movement of one of their hind-feet; and
when their backs are rubbed with a stick, so strong is the habit, that
they cannot help rapidly scratching the air or the ground in a useless and
ludicrous manner. The terrier just alluded to, when thus scratched with a
stick, will sometimes show her delight by another habitual movement,
namely, by licking the air as if it were my hand.

Horses scratch themselves by nibbling those parts of their bodies which
they can reach with their teeth; but more commonly one horse shows another
where he wants to be scratched, and they then nibble each other. A friend
whose attention I had called to the subject, observed that when he rubbed
his horse’s neck, the animal protruded his head, uncovered his teeth, and
moved his jaws, exactly as if nibbling another horse’s neck, for he could
never have nibbled his own neck. If a horse is much tickled, as when
curry-combed, his wish to bite something becomes so intolerably strong,
that he will clatter his teeth together, and though not vicious, bite his
groom. At the same time from habit he closely depresses his ears, so as to
protect them from being bitten, as if he were fighting with another horse.

A horse when eager to start on a journey makes the nearest approach which
he can to the habitual movement of progression by pawing the ground. Now
when horses in their stalls are about to be fed and are eager for their
corn, they paw the pavement or the straw. Two of my horses thus behave
when they see or hear the corn given to their neighbours. But here we have
what may almost be called a true expression, as pawing the ground is
universally recognized as a sign of eagerness.

Cats cover up their excrements of both kinds with earth; and my grandfather[116] saw
a kitten scraping ashes over a spoonful of pure water spilt on the hearth; so
that here an habitual or instinctive action was falsely excited, not by a
previous act or by odour, but by eyesight. It is well known that cats dislike
wetting their feet, owing, it is probable, to their having aboriginally
inhabited the dry country of Egypt; and when they wet their feet they shake
them violently. My daughter poured some water into a glass close to the head of
a kitten; and it immediately shook its feet in the usual manner; so that here
we have an habitual movement falsely excited by an associated sound instead of
by the sense of touch.

Kittens, puppies, young pigs and probably many other young animals,
alternately push with their forefeet against the mammary glands of their
mothers, to excite a freer secretion of milk, or to make it flow. Now it
is very common with young cats, and not at all rare with old cats of the
common and Persian breeds (believed by some naturalists to be specifically
extinct), when comfortably lying on a warm shawl or other soft substance,
to pound it quietly and alternately with their fore-feet; their toes being
spread out and claws slightly protruded, precisely as when sucking their
mother. That it is the same movement is clearly shown by their often at
the same time taking a bit of the shawl into their mouths and sucking it;
generally closing their eyes and purring from delight. This curious
movement is commonly excited only in association with the sensation of a
warm soft surface; but I have seen an old cat, when pleased by having its
back scratched, pounding the air with its feet in the same manner; so that
this action has almost become the expression of a pleasurable sensation.

Having referred to the act of sucking, I may add that this complex
movement, as well as the alternate protrusion of the fore-feet, are reflex
actions; for they are performed if a finger moistened with milk is placed
in the mouth of a puppy, the front part of whose brain has been removed.[117]
It has recently been stated in France, that the action of sucking is
excited solely through the sense of smell, so that if the olfactory nerves
of a puppy are destroyed, it never sucks. In like manner the wonderful
power which a chicken possesses only a few hours after being hatched, of
picking up small particles of food, seems to be started into action
through the sense of hearing; for with chickens hatched by artificial
heat, a good observer found that “making a noise with the finger-nail
against a board, in imitation of the hen-mother, first taught them to peck
at their meat.”[118]

I will give only one other instance of an habitual and purposeless
movement. The Sheldrake (Tadorna) feeds on the sands left uncovered
by the tide, and when a worm-cast is discovered, “it begins patting the
ground with its feet, dancing as it were, over the hole;” and this makes
the worm come to the surface. Now Mr. St. John says, that when his tame
Sheldrakes “came to ask for food, they patted the ground in an impatient
and rapid manner.”[119] This therefore may almost be considered as
their expression of hunger. Mr. Bartlett informs me that the Flamingo and
the Kagu (Rhinochetus jubatus) when anxious to be fed, beat the
ground with their feet in the same odd manner. So again Kingfishers, when
they catch a fish, always beat it until it is killed; and in the
Zoological Gardens they always beat the raw meat, with which they are
sometimes fed, before devouring it.

We have now, I think, sufficiently shown the truth of our first Principle,
namely, that when any sensation, desire, dislike, &c., has led during
a long series of generations to some voluntary movement, then a tendency
to the performance of a similar movement will almost certainly be excited,
whenever the same, or any analogous or associated sensation &c.,
although very weak, is experienced; notwithstanding that the movement in
this case may not be of the least use. Such habitual movements are often,
or generally inherited; and they then differ but little from reflex
actions. When we treat of the special expressions of man, the latter part
of our first Principle, as given at the commencement of this chapter, will
be seen to hold good; namely, that when movements, associated through
habit with certain states of the mind, are partially repressed by the
will, the strictly involuntary muscles, as well as those which are least
under the separate control of the will, are liable still to act; and their
action is often highly expressive. Conversely, when the will is
temporarily or permanently weakened, the voluntary muscles fail before the
involuntary. It is a fact familiar to pathologists, as Sir C. Bell
remarks,[120]
“that when debility arises from affection of the brain, the influence is
greatest on those muscles which are, in their natural condition, most
under the command of the will.” We shall, also, in our future chapters,
consider another proposition included in our first Principle; namely, that
the checking of one habitual movement sometimes requires other slight
movements; these latter serving as a means of expression.