We must picture to ourselves, then, in the animal organism, a multitude of nerve-fibres running inwards from all the end-organs of the special senses, from the muscles, and from the internal organs, and all converging on the central nervous system. And we must picture to ourselves a multitude of nerve-fibres passing outwards from the central system, and diverging to supply the muscles, glands, and other organs which are to respond to the stimulation from without. We must picture the fibres coming from or going to related parts or organs collecting together to form nerves and nerve-trunks, which are, however, only bundles of isolated nerve-fibres. And, lastly, we must picture the central nerve-system itself co-ordinating and organizing the stimuli brought into it by afferent nerves, from the organs of special sense, and handing over the resultants by efferent nerves to the organs of special activities. So far we have purely physiological effects, many of which occur with surprising accuracy and precision when an organism is in a state of unconsciousness. Place your finger in the palm of a sleeping child, and the fingers will close over it without the child awaking to consciousness. If, in a frog, the brain of which has been extirpated, the side be touched with a drop of acid, the leg of that side will be drawn up, and the foot will be used to wipe away the acid. And if that leg be held and prevented from reaching the side, the other leg will be brought round so as to try and bring the foot within reach of the irritated spot. The actions are, however, in all probability, purely physiological, and are performed in complete absence of consciousness. * * * * * When we turn from the physiological to the psychological aspect of the question, we enter a new world, the world of consciousness, wherein the impressions received by the recipient organs (no longer regarded as mere stimuli, but as the elements of consciousness) are co-ordinated and organized, and are built up into those sensations and perceptions through which the objects of the external world take origin and shape. It is with this process that we have now to deal; and we will deal with it first in man.