Emotion, as we have said, is a continuity of complex presentations whose elements are manifold; it is a state of feeling subject to constant modification and expansion while experience develops. First among the causal factors which influence emotion are the instincts, others may be intellectual concepts, many more come from the substrata of consciousness, and of these many are strictly physiological in character; for instance, there may be disturbances of the genital, vasomotor or digestive systems, cerebellar disturbances or latent molecular or biochemical nervous conditions, during which the mind responds to stimuli ignored under other or healthier circumstances; but over all it is the inherent disposition of the immaterial psychic or subjective mind which gives the whole its tone and tendency. We must, indeed, admit with James that "a disembodied human emotion is a sheer nonentity." With the psycho-physical problem as to whether sensory excitation is antecedent to emotional expression, or emotion gives rise to bodily expression, we are not here directly concerned. Since emotion is a continuous condition of experience, it may reasonably be supposed that organic disturbance is both a contributory cause and the reactionary result of emotion.[71] Most people admit that "each emotion is a resultant of a sum of elements," and that some of those elements are functional and organic, without admitting the contention of Professor James and those who insist with him that emotion is but a sum of organic sensations.[72] Emotional disturbances lead directly to the overthrow of the mental balance, which divides the normal man from the madman and the neurasthenic. Modern psychiatrists lay stress on the emotional character of the latter affection. The underlying features of "functional neurosis" reveal themselves in symptoms denoting the clash of emotional elements within, together with a corresponding lack of adaptability to outer environment, and are characterized by instability and exaggeration of emotion rather than impaired intellect.[73] The cultivation of the æsthetic, pleasurable and benevolent emotions on the one hand, and the elimination of violent emotional excitements or discordant and morbid emotions on the other, are conditions as essential for the physical health as for the happiness of the individual. Emotional sensibility is a condition necessary for the full appreciation and enjoyment of art, and of all that is pleasurable and beautiful, but when emotion is allowed to colour reason, the mind is closed to truth, knowledge and logic.