The Correlation of Mind and Body.-- It is of the utmost importance that the mutual reaction of mind and body upon each other should be thoroughly understood. This reaction is so constant, so intricate, and so complex that it is at times difficult to say which is cause and which effect. Does the depressed state of the mind cause the indigestion, or is a torpid liver the real seat of the melancholia? The brain is the most delicately constructed organ in the entire body. In the lower animals the brain is simply the great nerve-center which, with its prolongation the spinal cord, presides over all the functions of life which differentiate the animal from the vegetable. In the human being the brain is much more highly developed and complicated; and is, in addition, the seat of the mind, the intellect, and the affections. Like all the other tissues of the body, the brain receives its nourishment from the blood-vessels which pass through it, and its healthy maintenance is in a direct ratio to the condition of its blood-supply. A most interesting psychologic study is found in the case of cerebral paralysis of young children, where there is mental defect amounting to stupidity or imbecility, accompanied by extensive paralysis of the body, so that the child is not able to sit up. With the gradual improvement of the physical condition, so that the muscles become firm and the child can sit, stand, and even walk, there is a corresponding mental development; from being stupid and dull, the expression of the face brightens and becomes intelligent; the child talks quite as well as other children of its age, and sometimes becomes really intellectually precocious. Here we see the development of the brain as a direct result of the improved physical condition. In certain cases of insanity, on the contrary, we find that the wasting away of the body results from the disease of the brain, i. e., the disease of the brain has wrought the wreck of the body. From these pathologic studies, or studies of how the diseased state of the brain and body may be overcome by physical development, on the one hand, and, on the other hand, how the healthy body may be wrecked by disease of the brain, we will turn to a consideration of the effect of the development of the mind and intellect upon the physical health.