We often hear persons, speaking of some great fright, say: 'I was like one struck blind, I could see nothing.’ Travellers tell of serpents blind with fear, that bit the shadows and branches of the trees, blunting their teeth and shedding their poison fruitlessly. Darwin maintains that there are two distinct causes for the frown which every little difficulty in a train of thought produces. One is very similar to that propounded by Spencer, of which we have already spoken; the other runs as follows: 'The earliest and almost sole expression seen during the first days of infancy, and then often exhibited, is that displayed during the act of screaming; and screaming is excited, both at first and for some time afterwards, by every distressing or displeasing sensation and emotion,--by hunger, pain, anger, jealousy, fear, &c. At such times the muscles round the eyes are strongly contracted; and this, as I believe, explains to a large extent the act of frowning during the remainder of our lives.’[23] [23] Ch. Darwin: _The Expression of the Emotions_, p. 225. This explanation does not seem to me satisfactory, because it only pushes the question further back, and we must still ask: But why does the child frown when it cries? But, indeed, it suffices to render Darwin’s hypothesis improbable, if we call to mind that new-born children frown before they shed a single tear. The following is the explanation which I offer of this phenomenon. When we look intently at an object, we must contract all internal and external muscles of the eye. This is indispensable in order to effect the adjustment by which we modify the curvature of the lens in the interior of the eye; that is to say, we alter the lens according to the distance, in the same way as anyone looking through a telescope adjusts it by lengthening or shortening the tube. We have already seen that the pupil must contract when we contemplate an object close to us; thus we cannot direct our gaze towards our nose without a contraction of the pupil. The most important movement of the external muscles of the eye is that by means of which we produce a convergence of the visual rays from both eyes on the object of attention. Thus, whereas the two eyes are parallel when we are absent-minded or gazing into distance, they converge when fixed on an object near us, as the hands would meet in order to take hold of it. All these movements are effected by a single nerve, called the motor-oculi, between which and the facial nerve there is a certain sympathy, as may be seen in the unconscious movement of the eyelids and forehead when we exercise the eye. And _vice versa_, when we close the lids, we move the eyeball without intending to do so. We may convince ourselves of this if we hold one eye shut with a finger and then close the lid of the other; immediately we feel the eyeball under the finger turn downwards.