III
One of the reasons why the facial muscles move more easily, is their diminutive size. It was Spencer who first clearly developed this idea, and I know of nothing more fundamental in the language of the emotions. 'Supposing,’ he says, 'a feeble wave of nervous excitement to be propagated uniformly throughout the nervous system, the part of it discharged on the muscles will show its effects most where the amount of inertia to be overcome is least. Muscles which are large, and which can show states of contraction into which they are thrown only by moving limbs or other heavy masses, will yield no signs; while small muscles, and those which can move without overcoming great resistances, will visibly respond to this feeble wave. Hence must result a certain general order in the excitation of the muscles, serving to mark the strength of the nervous discharge and of the feeling accompanying it.... It is because the muscles of the face are relatively small, and are attached to easily moved parts, that the face is so good an index of the amount of feeling.’[19]
This law, however, is in my opinion insufficient to explain the expressions of the face, because we have very fine, small muscles in the ear, the skin, and elsewhere, that yet take no part in the expression, although the resistance they offer is very small.
Great importance must, I think, be attached to the continual use of certain muscles, and to the different excitability of their nerves. The muscles which we most frequently put into movement are also those which most easily betray the excitement of the nerve-centres. It is so with the ear of the horse and dog, which is a faithful mirror of everything they feel, of all their emotions; while the ears of man, although possessing the same muscles, remain immovable even during the strongest emotion, and solely because we never make use of them.
The facial muscles are agitated by every little shock which the nervous system receives, because they are already perpetually in movement in respiration, speaking, chewing, and in the defence and use of the organs of sense situated in the head. We very often meet people who, in consequence of increased irritability of the nerve-centres, suffer from nervous contractions of the face, which make them wink rapidly, contort the mouth and frown, but we never notice similar disturbances in hands or feet, or in any other part of the body.
The varying resistance which the different nerves of the organism oppose to the nervous currents is an important factor in expression. The proximity of the muscles of the face, and especially of the eyes, to the brain renders the nervous discharges easier. Death always begins in the parts furthest removed from the centre, the legs grow rigid sooner than the arms, and the eye is the last to be extinguished.
The subject at present under consideration is a field of study which physiologists have perhaps too much neglected. Johannes Müller,[20] the father of modern physiology, in speaking of those 'movements which depend upon mental conditions,’ expresses himself in the following manner: 'The extremely varied expression of the lineaments of the face in different passions, shows that, according to the various states of the mind, entirely different groups of fibres of the facial nerve are brought into activity. The reasons of this phenomenon, of these relations of the facial muscles to special passions, are totally unknown.’
Wishing to make a few experiments on the facial nerve, to see whether I should succeed in discovering anything in this obscure field of physiology, I laid bare the facial nerve, at its point of departure from the skull, in a dog rendered insensible with chloral, and then fixed two electrodes in such a manner that I was sure of being able to irritate the whole nerve by means of an electric current. While using irritants so weak that they were imperceptible on the tongue, I observed that they could cause a contraction of the muscles of the forehead and make the ears move, while the whole muzzle remained still as in an animal in an attentive attitude. When I used a slightly stronger stimulus, the muscles of the nose and eyelids and the zygomatic muscle moved; when the irritant was still more intensified, the muscles of the under-lip contracted and the mouth opened; while under very strong irritations, the dog assumed the fierce expression of one about to attack.
There is something fantastic in those experiments on decapitated animals of which the brain has been destroyed, and the face of which may be taken up in the hand like a mask of flesh. While applying an electric current to the motor nerves, one sees the features reanimate themselves, and a series of expressions pass over them one after another—attention, joy, rage, as though the electric apparatus applied to the facial nerve represented the commands of the brain or psychic impressions which in reality no longer exist.
The mechanical part of expression is, therefore, much simpler than one thinks. When a psychic operation takes place in the nerve-centres, the tension propagates itself along the nervous lines of least resistance. The more sensitive we are, the more graceful, beautiful, expressive, and fascinating is the curving of the lips produced by a smile. Peasants and coarse, dull persons cannot smile, with them the stimulus increases until it bursts out in a noisy, vacant laugh.
The nerve-paths are constructed in such a way that the brain does not need trouble itself about the muscular movements. It is the intensity of the excitement which produces the expression; the stronger it is, the more numerous are the paths through which the nervous tension forces its way; as it increases, it overcomes all obstacles and resistance confronting it in other paths impassable till that movement, and contracts muscles which till then had remained neutral.
The effects of the passions are reflected principally in the muscles of the face and respiration. No other function has to adapt itself more continuously than this last to the needs of the organism, standing as it does in close connection with all changes taking place in the nerve-centres. The muscles most vividly expressing passion are nearly all respiratory muscles.