As I write this, I have before me a very thin section of the brain, showing the nucleus of the facial nerve as it appears in man. It is a gray spot, as large as the head of a small pin, slightly spindle-shaped, and having a volume of about two cubic millimetres. If we look at it under the microscope we see nothing but an accumulation of cells, about the five-hundredths of a millimetre in diameter, and with delicate branches intertwining with each other. In vain the eye tries to find a path through this intricate network of filaments and cells; imagination loses itself as in a labyrinth, and we remain humbled and almost frightened at the thought that we are contemplating the corpse of the noblest part of the brain. The activity of these cells has roused the most powerful emotions of our life: our knowledge of men, our sympathy, indifference, suspicion were provoked by the movements which they gave to the faces of those we have known; friendship, affection, and the most holy joys of life brightened our countenance with a smile which came from these cells; they, again, diffused the shadow of sadness, pain, and tears--and all this drew life from a part of the brain so minute that by a mere touch we could unconsciously crush it. VI The greatest difficulties in the study of the alterations which the human face undergoes in suffering are essentially two in number. The first is the rapidity and the perpetual restlessness of muscular movements, which are so fugitive that our eye cannot grasp and comprehend them. The second difficulty lies in the nature of our mind, which is disturbed and touched at the sight of pain. Even men who have been hardened and accustomed to the sight of blood and of human misfortunes, are yet moved at the terrible picture of pain wreaking its rude will on a sensitive organism. Human pain is of such importance that all scientific curiosity becomes a trifling and ridiculous thing, and our mind rebels and feels an invincible repugnance to every desire which has not the alleviation of the sufferer for its object, to every act which does not spring from a lively and intense compassion.