Page:Mind (New Series) Volume 12.djvu/310

 296 W. MCDOUGALL : increased leakage through all the valves. Then after a certain number of gushes the water in the vessel will reach such a level that its pressure overcomes the resistance of the weakest valve, which therefore opens and allows the passage of a stream of water. If now the amount of water coming in at each gush be so great that it cannot at once be carried away through the valve of lowest resistance, the level of the water will rise with each of the inward gushes in spite of the opening of that valve until the pressure suffices to open one or more of the valves of higher resistance, when overflow into the corresponding vessels will occur. The valve lowest in order of resistance represents the synapse or synapses of the reflex path of level i., the valve next in this order repre- sents the synapses of the corresponding path of the sensory- reflex level, and the others various other junctions with paths of these two levels. The outflow through paths of levels i. and ii. is not con- fined to the motor nerves of skeletal muscles only, but finds its way in part to the efferent nerves of the viscera, increasing the tonus and contractions of arterioles, heart, lungs and perhaps other organs. During sleep these organs have been kept in a state of gentle regular activity, through a circular process of self-control ; their movements initiate an excite- ment of their sensory nerves which propagates itself through reflex paths of the cord and bulb and out along efferent nerves as a series of impulses which, returning to the same viscera, determine the initiation of a fresh afferent influx. On the in- cidence of the series of auditory stimuli this self-maintaining circular process is complicated and disturbed by a new series of efferent impulses, and the resulting changes in the visceral movements determine an increased afferent inflow which, as in the case described above, no longer finds a sufficient outlet through the reflex paths and therefore overflows to higher-level paths lying chiefly in the prefrontal cortex. The excitement of these paths is the physical basis of those obscure affections of consciousness from which the idea of the self is synthesised. So self-consciousness is aroused, and, owing to previous similar experiences, it takes the form of the idea of self-lying-in-bed, and this idea is intimately associated with that of the bed- room and the house in their spatial relations. Hence the excitement of those prefrontal paths, which determines the rise of self -consciousness, leads on to the excitement of that mental system or complex system of paths which is the physiological basis of the idea of the self-in-bed-in-my-own- house. These upper-level paths, being thus centrally excited, become paths of low resistance and therefore, when next