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Darwin attributed, I think, too much importance to the will considered as the cause of expression. We younger physiologists are more mechanical; we examine the organism more minutely, and it is in the structure of the organs that we seek the reasons of their functions.

I shall here give an example of this different way in which I have explained a few phenomena.

Rabbits are, as is well known, extremely timid animals, and it is remarkable that no other blushes and grows pale so easily as the rabbit. The changes in circulation produced by psychical impressions and by the emotions are more observable in the ears than in the face, as is indeed the case with many men. In Northern Italy, after someone has received a vigorous scolding, I have heard the popular expression used: 'He caught it hot enough to make his ears turn red.’ In the middle of the auricle of the rabbit’s ear there is an artery, running from the base to the summit, which ramifies and winds in such a manner as to form two veins on the edge of the auricle. In 1854, Moritz Schiff observed that this artery showed alternate movements of contraction and expansion, not corresponding to the systole and diastole of the heart. If one looks at the rabbit’s ear against the light, from time to time one sees the artery decrease in diameter, until at last it quite disappears, then it increases again, and, as it swells, it expands all its branches, so that the whole ear becomes of a vivid red and also warmer. This fulness of blood in the ear lasts a few seconds, then artery and branches contract and the redness gradually dies away. Schiff called this artery an accessory heart, because he imagined that the contractions and expansions observed by him in the vessels of the ear were to promote a better circulation of blood in the ear of the rabbit, just as the heart does for the rest of the body.

In repeating Schiff’s observations I used certain precautions which others would perhaps have thought superfluous. Instead of watching the rabbit while holding it in my hands, I thought to spare it all emotion, by enabling myself to observe the ears without its becoming aware of the fact. For this purpose I had a cage made in such a manner that it fitted exactly into the inside frame of a window, and whereas it was impossible for the rabbits to look into the room, I could watch quite easily, without being seen, through a few holes in the cage. By means of this simple arrangement I could observe the rabbits at my leisure, and study their habits while they were quiet, without a suspicion that they were being noticed. The first time that I so watched them, I saw, to my surprise, that the ears were no longer so red as when the animals were startled by feeling themselves seized and held fast in my hands on the table. The rapid movements of dilatation and contraction in the blood-vessels of the ear, the sudden blushing and loss of colour so characteristic of the timidity of these animals, were no longer observable. The artery of the ear remained dilated and of a vivid red for a long time, often for hours. I noticed this especially in summer, when the animals were uniformly tranquil. A state of absolute repose, however, is not always accompanied by an expansion of the blood-vessels. All rabbits have not ears equally red or pale at the same time and under the same conditions. A similar circumstance may be noticed at any time in the faces of men. Young rabbits blush more easily than old ones. Often while watching the buck and doe with the young ones, one could see the ruddy ears of the latter turn pale every now and then, while the former, like old people with us, remained calm and had pale ears. But even amongst the young ones of the same litter, one finds considerable differences in the facility for blushing.

At the market I chose those animals that blushed most easily and frequently, just as the slave-dealer picks out for the harem those women who charm by blushing more vividly than the others. If one studies attentively the loss of colour in the ears of a rabbit when perfectly quiet, one can nearly always discover the cause in some external circumstance. Often while the animal has red ears and is breathing quietly, one notices a sudden change in the rhythm of respiration; the rabbit lifts its head, looks around, or sniffs; a contraction of the blood-vessels follows, and the ears become pale. After a few minutes, if nothing happens, the ear becomes red again. Any noise causes renewed pallor. A whistle, a cry, a sound of any kind, the bark of a dog, a sunbeam suddenly penetrating into the cage, the shadow of a swiftly passing cloud, the flight of a distant bird, each suffices to produce a rapid loss of colour in the ears, shortly followed by a more vivid flush. We may therefore maintain that the circulation of blood in the ears reflects the psychic condition of the animal, and that nothing takes place either in itself or in its surroundings without immediately acting upon these blood-vessels.

Thus the fact observed by Schiff receives confirmation, but the explanation which I give of it differs from his. The dilatation and contraction of the arteries in the rabbit’s ear can no longer be compared to the movements of an accessory heart, and, in my opinion, correspond to the colour or pallor of the human face. In this manner the phenomenon is deprived of the exceptional character with which it was introduced into science, and takes its place amongst those observable in man and nearly all animals.

We may see the same phenomenon noticeable in the rabbit’s ear, in the cock’s comb and wittles; during emotion the fleshy protuberances and the skin on the neck of the turkey distinctly blush and grow pale, and in men and dogs not only the face but also the feet are subject to these changes of colour.

These things were unknown owing to insufficient observation. It was thought that animals did not blush, because the blood-vessels of their skin lie concealed under hair, feathers, or scales, and because the epidermis is less transparent and the pigment cells more abundant in the lower layers of the skin. And so blushing was deemed a privilege of man, which, however, is not the case. It suffices to study the face of the rabbit attentively in order to see that it is very sensitive, even to the slightest impressions. If one looks carefully at the nostrils and lips, considerable variations in the colour may be observed, corresponding to those occurring at the same time in the blood-vessels of the ear. These phenomena became so familiar to me during my study of rabbits, that I needed only observe the muzzle of the animal, and more particularly the tip, in order to know at once whether the ears were at that moment pale or red. This certainty was in part due to the alteration in the rhythm of breathing and in the movement of the nostrils produced by the slightest emotion, as also in man.