On the other hand, a destructive lesion may be so placed in the spinal cord or brain as to allow centripetal impressions to reach healthy spinal gray matter in the normal way, but preventing their passage frontad (upward) to be recognized by consciousness. In such a case we observe normal, or more commonly exaggerated, reflex action in parts which are insensible in the ordinary sense of the term. Indeed, in many cases the disconnected caudal portion of the spinal cord is in a state of vastly exaggerated reflex activity, as shown by the tetanoid and convulsive involuntary and reflex movements which take place in completely paralyzed and anæsthetic limbs (paraplegia from transverse myelitis). In general terms, it may be stated that when anæsthesia is due to lesions of peripheral nervous endings, of nerve-trunks, and of the posterior root system of the spinal cord, reflexes are diminished or lost. It is often stated that anæsthesia causes ataxia of movement. This, from the results of experiments on animals and from clinical study, we believe to be a gross error. In animals and in man loss of sensibility gives rise to awkwardness or uncertainty in movement (increased if the eyes be closed) which is properly to be classed as a special variety of inco-ordination; but it is not from ataxia, in which irregular, jerky, oscillating motions occur when a volitional act is attempted, these movements resulting from want of harmony in the action of antagonistic muscles which in the normal educated state automatically act together to produce the desired result. Besides, we occasionally observe cases of typical spinal ataxia in which no impairment of sensibility can be observed. THE TOPOGRAPHICAL DISTRIBUTION of alterations of sensibility requires careful determination in practice, as from it we obtain most valuable aid in diagnosis. The following are the principal types observed: (_a_) Alterations of sensibility in one lateral (vertical) half of the body and head. We thus have hemihyperæsthesia, hemiparæsthesia, or hemianæsthesia, and the special senses on one side are frequently involved. This clearly hemi-distribution indicates that the lesion or functional disorder is in the cerebral hemisphere of the opposite side, more especially in the caudal segment of the internal capsule or in its areas of cortical distribution (occipital, temporal, and parietal lobes). The distribution of hemianæsthesia, etc. from organic disease in these parts is identical with that observed in some functional (hysterical) cases; we can make the diagnosis only by the help of other data. If the sensory disorder does not affect the head, but is limited to one {38} lateral half of the body, it is, if due to organic disease, quite certainly of spinal origin.