148. At the opening of this chapter mention was made of the besetting sin of the analytical tendency, namely, to disregard the elements which provisionally had been set aside, and not restore them in the reconstruction of a synthetical explanation. Familiar experiences tell us that a stimulus applied to the skin is followed by a muscular movement, or a glandular secretion; sometimes this takes place without any conscious sensation; sometimes we are distinctly conscious of the stimulus; and sometimes we consciously will the movement. These facts the physiologist tries to unravel, and to trace the complicated processes involved. The neurologist of course confines himself exclusively to the neural processes; all the other processes are provisionally left out of account. But not only so: the analytical tendency is carried further, and even in the neural process the _organs_ are neglected for the sake of the nervous _tissue_, and the nervous tissue for the sake of the _nerve-cell_. The consequence has been that we have an explanation offered us which runs thus:-- 149. The nerve-cell is the supreme element, the origin of the nerve-fibre, and the fountain of nerve-force. The cells are connected one with another by means of fibres, and with muscles, glands, and centres also by means of fibres, which are merely channels for the nerve-force. A stimulus at the surface is carried by a sensory fibre to a cell in the centre; from that point it is carried by another fibre to another cell; and from that by a third fibre to a muscle: a reflex contraction results. This is the elementary “nervous arc.” But this arc has also higher arcs with which it is in connection: the sensory cell besides sending a fibre directly to a motor cell, also sends one upwards to the cerebral centres; and here again there is a nervous arc, so that the cerebral centre sends down an impulse on the motor cells, and the contraction which results is due to a volitional impulse. The transmission of the stimulation which in the first case was purely physical, becomes in the latter case psychical. The sensory impression is in one cell transformed into a _sensation_, in another cell into an _idea_, in a third cell into a _volition_.