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O long as the mind was regarded as something separated from the body, or only united to it by feeble ties, bodily conditions could have nothing to do with mental phenomena—insanity was a disease of the soul. The monk, standing over a miserable lunatic chained to a staple in the wall, and flogging him in order to make him cast his devil out, was a logical outcome of this hypothesis. The union of psychology and physiology is the closing of the circuit, in one direction, of the pursuit after knowledge, and marks the initiation of a rational comprehension of the mind and of its relation to corporeal conditions. How such mistaken ideas of the word melancholia, as those entertained by the monk in his capacity of physician for diseases of the mind, could have attained their sway in the face of the maxim mens sana in corpore sano, only becomes intelligible when we remember the ignorance, the superstitious prejudices, the contempt for knowledge of the natural man, which found their highest expression during the monkish supremacy of the dark ages. Slowly but surely was the emancipation of the intellect from the fetters of priestly tyranny achieved. The days of the minor Trinity—the soul, the mind, and the body—are numbered; the advent of a physiological psychology is at hand. That insanity which was regarded as an indication of some disease of the soul, in whose production the body had no share, is now known to be linked with appreciable pathological changes, and in many instances is amenable to physical remedial agents. Thought is the product of the cells of the gray matter of the brain—the result of a change of form in inorganic matter taken into the system as food, of which acids and other products of oxidation, of retrograde tissue-metamorphosis, are the waste.

Such being the case, it is obvious, then, that bodily conditions will affect the nutrition of the brain, or rather of the cerebral cells, and so modify their products. It is not necessary to go into the more pronounced conditions called insanity for the evidences of such influence; they are to be found in the varying mental attitudes of common life. It is true, however, that the study of the more marked cases furnished by insanity, with their deeper shadows and clearer definitions, is the best preparation for the proper recognition and discrimination of the finer shades, the slighter changes, which exist among the sane. More especially is this the case in attempting to analyze the varying emotions. At one time all looks bright, cheerful, and encouraging; at another, the same prospect looks cheerless and tinted with despair.