The eyeballs are functionally suspended in the labyrinth as in a gyrostat. From this point of view, the laws of Ewald and Flourens may be summarized as follows: The eyeballs are carried by the current of endolymph; this is the slow phase of nystagmus. The quick phase is in the opposite direction. In a normal individual, every movement of the head is connected with a corresponding stimulation of the whole vestibular system. Irritation of the vestibular apparatus which does not correspond to the adequately apportioned work of the muscles (movement of the head) causes a feeling of vertigo. When the stimulation of the vestibular apparatus creates a sensation of vertigo in the plane perpendicular to the vector of gravity, no inclination or postural reaction follows. When the plane of the created vertigo is not perpendicular to the vector of gravity, then there appear inclination reactions and sometimes very marked postural reflexes. Caloric stimulation unconnected with corresponding movements causes vertigo. A vertigo caused by caloric stimulation, which affects only a part of one of the vestibular apparatuses, cannot be organized as a vertigo in the plane perpendicular to the vector of gravity. Hence, under proper conditions of observation, we can ascertain the appearance of inclination of the head and trunk. When considering the conditions of the flow of endolymph in the different canals and the relation of the flow to the neuromuscular apparatus, we see how the question of the planes of symmetry or asymmetry of the body widens out and becomes important in some vestibular problems. Certain movements of the body and eyeballs are reciprocal; others, because of anatomical and functional asymmetry, are not reciprocal. These relations give some insight into the problem of the compensation phenomena.