It will perhaps render our thinking more accurate if we attempt to get a clear idea just here as to what consciousness is and what it is not. Various definitions of the term have been given, but the simplest and truest seems to be that it is a knowledge of the present existence of self, and perhaps also of surrounding objects, although it is conceivable that a conscious person might be shut off from all contact with the external world by abolition of the senses. Consciousness is certainly not what the philosopher and the theologian call the Ego, or the personality of the individual. A blow on the head puts an end for the time being to consciousness, but not to the man's personality. Neither is consciousness the same as the sense of personal identity, although it is closely connected with it. The conviction of a man that he is the same person through the manifold changes which occur in him as the successive years go on is evidently based on consciousness and memory. This is well illustrated by some very curious cases in which the sense or knowledge of personal identity has been completely lost. Not long ago an instance of such complete loss was recorded by Doctor Hewater (_Hospital Gazette_, November, 1879). The gentleman who was the subject of this loss found himself standing upon the depot-platform in Belaire City, Ohio, utterly ignorant of who he was or where he came from or where he was going to. He had a little money in his pocket, and in his hand a small port-manteau which contained a pair of scissors and a change of linen. He was well dressed, and on stating at the nearest hotel his strange condition and asking for a bed, was received as a guest. In the evening he went out and attended a temperance lecture. Excited by the eloquence of the speaker, he was seized with an uncontrollable impulse, rushed from the room and began to smash with a club the windows of a neighboring tavern. The roughs ran out of the saloon and beat him very badly, breaking his arm: this brought him to the police-station, and thence to the hospital. For months every effort was made to identify him, but at the date of reporting without avail. He was known in the hospital as "Ralph," that name having been found on his underclothing. His knowledge upon all subjects unconnected with his identity is correct: his mental powers are good, and he has shown himself expert at figures and with a pen. For a long time it was thought that he was feigning, but every one about him was finally convinced that he is what he says he is--namely, a man without knowledge of his personal identity. This curious case, which is by no means unparalleled in the annals of psychological medicine, shows how distinct memory is from consciousness. Memory of the past was in Ralph entirely abolished so far as concerned his own personality, but consciousness was perfect, and the results of previous mental training remained, as is shown by his use of figures.