The muscles of the eye contract also when we exert ourselves; for instance, if we try by night to look at a small distant light, at the same time lifting a heavy weight, or exerting ourselves in some other way, we see the light double, owing to the involuntary convergence of the eyes. I have photographed several persons during physical exertion, and many of them have quite the appearance of suffering, so pronounced is the contraction of the muscles of the forehead, although it was quite unnecessary. The arrangements of our organism are such that the energy, the tension of the nervous system diffuses itself in various directions, without the possibility, in certain cases, of restricting its influence to limited muscular groups. Thus, if we try to move the ear, the muscles which raise the corner of the mouth also contract; if we merely tell someone to close his eyes, we see the other facial muscles move, often causing involuntary grimaces. Again, we cannot move one eye to the right and the other to the left. Very few can turn the pupil upwards without raising the eyelids, or move the eyebrows separately. All this is due to the difficulty of localising the action of the will in the nervous fibres leading only to certain muscles; several groups of fibres seem always drawn simultaneously into the sphere of action, except when there has been much practice in discerning and selecting the fibres which shall accomplish an isolated movement, or when an intentional effort is made, which, however, is a matter of much difficulty. When animals look attentively at some object, they turn their ears towards it. This movement, which they make in order to collect the sounds, must be preceded by a contraction of the muscles of the forehead and of those serving to turn the auricle of the ear. It is very probable that these movements, noticeable also in monkeys, have been preserved in man, although in attention he no longer moves the ears but only the muscles of the forehead. In our nature psychic processes are so closely connected with their external sensory manifestations that it is impossible to check the manifestation of nervous activity in the muscles whenever the ideas appear to which these external movements stand in a permanent relation, even when this external communication is quite unnecessary. Thus we see that a man lost in thought gesticulates, making a hundred involuntary movements, and sometimes speaks, although no one is with him to whom he need communicate his ideas. And so it happens that we reproduce the characteristic movements of attention in forehead and eye whenever, in the various contingencies of life or in the development of ideas, an obstacle hinders the progress of thought. As soon as we begin any work which demands greater force of attention and reflection, we immediately and involuntarily put into action the mechanism of forehead and eye, which has always been made use of in intently scrutinising objects. IV