It is a clinically well-known fact that focal processes in the cerebrum above the level of the thalamus opticus may often lead to the occurrence of a crossed hemihypalgesia. The interpretation, however, of the disturbance in pain sense in such cases is frequently difficult, for repeatedly it is not so much—or not predominantly—the pain sensation itself that is disturbed; rather, indeed, it is the (secondary) experiencing of pain, by disturbances in attention or a change in psychic attitude toward pain in general. If this is the case, then a distinct localizing significance cannot be attributed to the symptom of hemihypalgesia. Besides, however, a relatively small group of suprathalamic focal processes showing crossed hemihypalgesia occur in which the pain conduction—or the primary identification of pain stimuli, as the case may be—seems to be essentially disturbed. This disturbance generally is transient in nature. For our problem, those cases especially are important in