Dangers of Over-attention.--The danger of concentration of mind on one's self, quite as much as on any other subject, becomes clearer when this theory is accepted as explaining the physical basis of the mental operations involved in attention. If people allow thoughts of themselves and of their physical processes constantly to occupy their minds, gradually that portion of the brain ruling over these becomes over-fatigued and fails to respond to the calls for relaxation. Insomnia may develop readily as a consequence of continued solicitude and prove to be, as the worst forms of insomnia so often are, quite unamenable to direct drug treatment, because, even during the enforced sleep that comes from drugs, dreams with regard to self and the supposed ills may still occupy the overworked portion of the brain. Nervous people are, most occupied with those parts of the brain which have something to do with the omission and transmission of trophic influence to particular parts of the body. As a consequence of the persistent hyperemia, too many trophic impulses are sent down. These cause an exaggeration of physiological function, in the stomach, the heart, or some other important organ. Hence these organs may become oversensitive. For all these reasons, this theory of attention, of the great Spanish {126} investigator, deserves to be well known by those who hope to treat neurotic affections, especially functional diseases of the brain, and therefore I prefer once more to give it in his own words. [Footnote 16] [Footnote 16: _International Clinics_, Vol II, Series 11.] Ramon y Cajal's Theory of Attention.--Under usual conditions, the motor apparatus of the gray matter suffices for the explanation or the varied course of association of ideas and of the reaction produced by voluntary motion. But as soon as attention is concentrated upon an idea, or a small number of associated ideas, there enters into the problem, besides the active retraction of the neuroglia of the corresponding part of the brain, a new factor--the active congestion of the capillaries of the over-excited region. As a consequence of this, the energy of emotion reaches a maximum. The heat and metabolism of the hyperemic parts is increased, which, of course, makes these parts capable of more work. [Illustration: FIG. 19.--NEUROGLIA CELLS OF THE SUPERFICIAL LAYERS OF THE BRAIN FROM AN INFANT AGED TWO MONTHS (method of Golgi). A, B, C, D, neuroglia cells of the plexiform layer; E, F, G, H, K, R, neuroglia cells of the second and third layers; I, J, neuroglia cells with vascular pedicles; V, blood-vessel. (Ramon j Cajal.)]