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. V Many may regret that such a characteristic difference between man and the other animals should be effaced, and that we should try in cold blood to prove that what is most noble, beautiful, and human in our countenance, we have in common with the brutes. But we console ourselves with the reflection that poetry, enthusiasm, inspiration and passion rise again under new and stronger forms in the contemplation of reality, that in the search after truth there lies a fascination which beautifies and ennobles the human intelligence, and that sentiment is never extinguished by any advance of science. To-day, when the experimental method is spreading so rapidly, it behoves us physiologists to be humble and to ask for hospitality in the studio of the artist, in the libraries of men of letters, in the drawing-rooms of cultured people, in order to diffuse the elementary principles of our science. The time has come when we must throw off our professorial robes, tie on our aprons, roll up our sleeves, and begin the vivisection of the human heart according to scientific methods. Let the artist no longer confine himself to a blind imitation of nature, to a perpetual reproduction on canvas, in marble, or in books of the phenomena and forms of life; he must know the why and wherefore of things, completely or in part, the connection between cause and effect; he must convince himself that nothing is the result of chance and that there is a reason behind every phenomenon. Blushing--that ideal token of innocence and purity--is no accidental fact; it was not given to man as a sign of nobility, nor as a mirror to reflect the agitation of his heart; it is a fact rendered necessary by bodily functions and which the will can neither produce nor suppress. It is simply caused by the structure of our vital machine, by the activity of the blood-vessels in all organs and in all animals.