If one speaks to a person while he is lying on the balance horizontally, in equilibrium and perfectly quiet, it inclines immediately towards the head. The legs become lighter and the head heavier. This phenomenon is constant, whatever pains the subject may take not to move, however he may endeavour not to alter his breathing, to suspend it temporarily, not to speak, to do nothing which may produce a more copious flow of blood to the brain. It was always a pleasant sight to my colleagues, visiting me during my researches, when they found some friend or acquaintance sleeping on the balance. In the afternoon hours, which I preferred for my investigations, it often happened that one of them would grow drowsy, and be rocked to sleep by the uniform oscillation of this scientific cradle. Scarcely had some one about to enter touched the handle of the door, than the balance inclined towards the head, remaining immovable in this position for five, six, and even ten minutes, according to the disturbance produced in the sleep. Often, after waking, the blood was no longer distributed in the same manner; the weight _R_ had to be moved towards the feet, from which an amount of blood had retreated in order to circulate more actively in the brain. The subject would then gradually grow drowsy again, and the balance incline towards the feet, the blood flowing, so to speak, from the centres of activity, and collecting in the veins of the feet. The weight _R_ had now to be moved in the opposite direction, until, in sound sleep, that distribution of the blood took place which is peculiar to this state of our organism. In the meantime the respiratory oscillations continued. Then, when all was quiet, one of us would intentionally make a slight noise, by coughing, scraping a foot on the ground, or moving a chair, and at once the balance inclined again towards the head, remaining immovable for four or five minutes, without the subject’s noticing anything or awaking. And also, when all was silent in the still hours of night, or during an afternoon sleep, one often noticed, without the appearance of any external cause, oscillations, as it were spontaneous changes of locality of the blood, arising from dreams or psychic conditions acting on the vaso-motor nerves and modifying the circulation, without the participation of consciousness, or at least without a trace of these processes remaining in the memory. IV