The enormous difference between the mind of a man and that of a child exists because in the latter the upper story of the brain is not developed, the convolutions are scarcely indicated, the organs of will and speech are wanting. As the large pyramidal cells appear and increase, the child acquires intelligence and speech; connections are established with the lower story in order to set muscles and organs which were before inactive into movement. But the difference between these two stories of nerve-centres continues during the whole life. I shall explain this by a few examples. A man is paralysed in consequence of some injury which prevents the upper story of his brain from communicating with the spinal cord. Hands and arms no longer move under the influence of the will, but when some long-expected person appears, or some sudden shock is given to the emotional sphere, he will be able to lift his arms. There is a paralysis of the facial nerve in which the voluntary closing of the eye is impossible, but if anyone makes a movement, as though he were going to poke his finger into the eye, the lid closes instantly. Later, we shall instance men who have remained dumb for a long time, and have regained their speech in consequence of a fright. Dogs deprived of a large part of the upper story of the brain make no sign of recognition when they see themselves threatened by the whip, but if it is cracked they scamper off hurriedly, or rush forward at it. A mouse with its hemispheres and optic thalami removed remained undisturbed by every noise but that resembling an approaching cat, when it jumped and fled. By means of injuries to the brain physiologists can easily check the activity of certain voluntary movements. If the peduncles of the cerebellum and certain points of the cerebrum are injured, dogs can be made to go either only to the right, or to the left, continually backwards, or in a circle, as though they were in a circus. The will of the animal is still in existence, but all his efforts are, as often with us, fruitless. In spite of himself his body is drawn in the direction determined by the lesion of the nerve-centres. Claude Bernard tells of a brave old general who, by a cruel irony of fate, could only march backwards.