We have been dealing up to the present with the normal activity of the cerebral cortex. It was noticed in passing, however, that the experiments to which our animals were subjected led in some instances to chronic disturbances of this normal activity. This was especially liable to occur in the early stages of our work, since in planning the experiments we had at first not even the slightest idea as to the limitations and the natural resistance of the cortex. The present lecture will be devoted to a description of those disturbances in the higher nervous activity which are of a purely functional origin, and not due to surgical interference or trauma. From some of these disturbances the animal recovers gradually and spontaneously under the influence of rest alone, on discontinuance of the disturbing experiments; in other eases the disturbances are so persistent as to require special therapeutic measures. In many instances we were able to make observations during the actual period of transition from the normal physiological state of the cortex to a pathological state, and then to study its therapy. The pathological state of the hemispheres in different individual animals from the action of injurious influences varies greatly.