Artificial stimulation or lesion of the semicircular canals or otolith organs in animals tends to produce certain unexpected reflex movements of the body which the animal tries to counteract voluntarily, so that all kinds of unusual movements are observed. If these organs are destroyed, one source of information about the position and the movements of the body is lost. This loss is not very serious in man, in whom it occurs as a result of diseases of the ear; man can obtain his orientation from visual, kinesthetic, and pressure sensations in spite of this loss. It is far more serious in aquatic and flying animals. Pressure differences are of no account when the body has nothing but water or air on all sides. In a greater depth of water vision is practically impossible. Under these circumstances the semicircular canals and the otolith organs are highly important for an animal’s life. Unfortunately no definite names have thus far been adopted for these senses. They are frequently called the static sense or the sense of equilibrium. But these names are of doubtful value, since other senses too may inform us about our equilibrium. The enumeration of our senses is not yet completed. What is hunger? What is thirst? What is nausea? These mental states are certainly similar, in some respects, to tones and odors. They are sensations. There is the difference, however, that we do not project them into external space, but think of them as characteristics of our own body’s condition. How is consciousness of these sensations brought about? No doubt, in a manner similar to that of the mediation of such sensations as odors and tones: through the stimulation of sensory neurons and the propagation of nervous processes toward the motor points of the body. The place of stimulation must be somewhere in our organs of nutrition, and thus these organs must be regarded also as a kind of sense organ. That the sensory function can be attributed to an organ in addition to another function has been proved by the example of the skin, muscles, and joints. The same may be said of other organs, for instance the lungs giving us the sensation of suffocation. We possess, therefore, a large number of organs whose primary function is of an active kind, but which also give information as to the condition of those active functions. The sensations resulting from them are as independent of each other as tones are of color or taste. But they do not permit of as many subdivisions as the sensations of the so-called higher senses. For the emotional part of our mental life they are of the greatest significance. Since we do not project them into the external world, but think of them as significant of the functions of our internal organs, they are rightly called by the common name of _organic sensations_. 2. _The Other Sensations_