APHASIA, or loss of the faculty of language, is so important a symptom as to deserve elaborate consideration in a separate article of this volume; and to it the reader is referred. Suffice it here to state that aphasia may be classified into three forms: (1) Sensory aphasia, in which there is primary disorder of the psycho-sensory (perceptive or centripetal) part of the complex central mechanism for speech; (2) Motor aphasia (including ataxic aphasia), in which the primary lesion affects the motor (expressive or centrifugal) parts of the mechanism; (3) Amnesic aphasia, in which loss of memory (effacement of residua) of words and signs is the prime condition. II. Sensory Symptoms. HYPERÆSTHESIA is a condition of exalted excitability in the various parts of the sensory apparatus: terminal nervous organs, nerve-trunks, central gray matter. We may admit such a state as existing {32} independently of consciousness, as where a lesion cuts off communication between the perceptive cerebral centres and the periphery, but in practice we consider only conscious hyperæsthesia. In this state the subject may be able to perceive (feel) slighter impacts than would affect a normal individual, or he receives an exaggerated, usually unpleasant, impression from ordinary excitations. It may also be said that hyperæsthesia exists as a purely subjective state, psycho-sensory hyperæsthesia, without external mechanical excitations. (_a_) Hyperæsthesia of common tactile sensibility in the skin and mucous membranes is frequent. The least touch is felt with unpleasant acuteness and causes unusual reactions of a reflex order; frequently, but not necessarily always, a sensation of pain is produced at the same time. It has been claimed that in certain cases the points of the æsthesiometer could be perceived (distinguished as two points) at smaller distances than the average normal, but I have never been able to demonstrate this to my satisfaction. The simplest form of tactile hyperæsthesia is met with in persons of a highly nervous organization, in those under the influence of strong emotions, in the hypnotic state, and while intoxicated. The common pathological conditions in which increased sensibility is found are meningitis (cerebral and spinal), hydrophobia, tetanus, neuritis, dermatitis, hysteria, and spinal irritation; also in connection with inflammations and traumatisms.