must be committed to specific centers which act with automatic certainty and never sleep.
Pursuing this line of inquiry, a third important step was taken by establishing the separate and automatic functions of the sensory ganglia at the base of the brain and the summit of the spinal column. Impressions from the surface reaching the spinal centers are passed upward to the sensory ganglia, and there give rise to sensations and emerge into consciousness, reflex action being here extended to conscious movements. Dr. Carpenter did much to unravel this branch of the subject about 1850, and his work on "Mental Physiology," published within a few years, will be found full of interesting and important information in relation to it. The problems entered upon were, of course, of great complexity, obscurity, and difficulty. Dr. Laycock had carried the doctrine of reflex action into the cerebral hemispheres, and shown its importance in the higher operations of the mind; and it yet remains a sharply debated question among nervous physiologists how far the principle of automatism extends in the higher realm of our psychical life.
It was thus gradually established that all mental operations, all thought, feeling, instinct, and volition, are the results, first, of the activity of the primary nervous elements, cells, and fibers, by which nervous influence is accumulated and discharged; and, second, of the interaction of numerous automatic centers variously endowed, but communicating with each other solely by the transmission of nervous force. The gain thus secured to mental science on its practical and progressive side was very great. The subject took its place among the definite and experimental science of the natural world. Nothing is so vague as the conception of mind from the metaphysical point of view. Quantitative results are unattainable by that method, and all limitations are scorned by it as degrading to the dignity of spiritual being. But in inquiring into the functions of the nervous system we are at once deeply involved in the physiology of limitations. Mind-force can not come from nothing, any more than other forms of force, and here as elsewhere one effect is at the expense of another. Thinking and feeling exhaust the mechanism, and we are involved with practical questions of waste and repair, exercise and rest, food, blood, nutrition, and the hereditary qualities of the nerve-centers.
Here also the study of mind widens out into the comprehensiveness of a true science by including all the grades of animal life as objects of psychological study. For here as well as everywhere else the higher is to be interpreted by the lower, the complex by the simple, and no animate creature is so far down in the scale that it does not illustrate some phase of mind which has a bearing upon the mental problems of higher beings. The introspective method of course breaks down here. Confined to the adult mind, it excludes the minds of children, and therefore the study of the laws of mental growth; confined to the human mind, it excludes those of all inferior beings. Yet when it becomes a question of determining the properties of nerve-centers, the nature of reflex action, of instinctive movements, and all forms of the laws of intelligence, then comparative psychology makes invaluable contributions to mental science.
And there is still another division of the study of mind of supreme importance, to which very little was or could be contributed by the old method, but which is making marked progress by the more recent methods of investigation: we refer to the subject of insanity. When we come to mental derangements, introversive study is obviously fruitless, and so long as that was pursued nothing was known of the nature of insanity. Mental disease in