THE OBJECTIVE APPROACH the objects presented by nature for our contemplation are living things endowed with powers which call for explanation. Vital functions, externally observed, consist primarily in movements. Movements, then, constitute our data and so far psychology would conform to the traditional dynam ical scheme of the natural sciences as a whole. The activities with which we are concerned can be arranged in hierarchical order, the lowest being found in all, even the simplest forms of life ; the highest, only in beings of a very elaborate type. Nowadays, the distinction between the higher and lower functions would receive an evolutionary interpretation, but the older, Aristotelian, way of defining it has also important implications : the lower, whilst presupposed by the higher, may occur in independence. Among the former are the processes of metabolism which result in self-conservation and growth, by reference to which the animate is defined. The cycles of self-conservation are repeated in move ments of a higher order, in the grosser movements of a body supplied with organs and limbs. In the higher organism we find complex forms of behaviour involving a sensitive and discrimi nating responsiveness to stimuli and more highly organized move ments which, whilst maintaining a general self-conserving ten dency, appear as the intelligent pursuit of widely differentiated ends. The hierarchy appears to be continuous, but whilst the lower functions fall clearly within the province of biology, the higher are more particularly what interest the student of psy chology. Rigid demarcations are out of the question. The most that can be said from this point of view is that the psychologist commences higher up the scale, whilst the biologist is working down to foundations. The psychologist follows on a higher level, or perhaps he starts with the biological data most explored, and works in the other direction, linking up the line of explanation to the facts of those who are working higher still. Such is the programme from the objective point of view.
potential energy expended in movements which directly or indi rectly are the means of restoring the balance of energy so ex pended. This is self-conservation at a higher level.
The abstract unit of this secondary type of self-conserving system is the response to stimulation, based on a structural coun terpart—the simple reflex arc. Three essential components are here involved, a specific receptive organ, a conductive neural bond, and a responsive muscle or gland. Receptor, Conductor and Ef fector are thus invariably to be sought in the interpretation of conduct. The receptors, which in their higher elaborations con stitute the sense organs, are primarily specialised structures with delicately selective sensitivity to certain forms of stimulation. As contrasted with the generalized responsiveness of undifferenti ated protoplasm each type of receptor has a "lowered threshold" to some specific "adequate" stimulus, such as heat, light or sound. The conductive filaments consist of chains of elongated neurones periodically interrupted by points of junction, the highly impor tant "synapses" through which the receptor not only gains com munication with its "own" effector, but also becomes functionally integrated in the system as a whole. The process terminates in contractile or secretory organs, stimulation thus evoking two dis tinctive modes of response—movements proper and glandular activities. The latter is an important element in emotional excite ment. The two reactions are neither independent nor mutually exclusive. They are quite frequently combined. Earlier studies of reflex action led to an over-emphasis of the fixity and the inevitable character of the response, but neither feature would seem to be invariable or of fundamental importance. The total organization is of an extremely labile constitution, adaptable in the extreme and subject to various forms of inhibition and con trol. "Volitional" so far from being opposed to reflex action emerges from it by progressive integration.