(7) Toxic narcosis, from opiates, morphia, chloral, etc., are often difficult of diagnosis, except that from opiates and morphia, in which extremely slow respiration and contracted pupils, with lowered temperature, point at once to the cause. In studying cases of coma all the above-enumerated symptoms should be considered as of great negative or positive value: often the diagnosis is only made by exclusion. The Cheyne-Stokes respiration, pupillary variations, differences in pulse-rate and volume, are present in such varied conditions, irrespective of the nature of the lesion, as to render them of minor value in differential diagnosis. DOUBLE CONSIOUSNESS is a rare condition, in which the subject appears to have separate forms or phases of consciousness, one normal, the other morbid. This occurs in hypnotic and somnambulic states, probably also in certain cases of insanity and epilepsy. The current of normal consciousness is suddenly broken; the patient enters into the second or abnormal state, in which he acts, writes, speaks, moves about with seeming consciousness; but after a variable time a return to normal consciousness reveals a break in the continuity of the memory: the patient has no recollection whatever of what he did or said in the morbid period. In the hypnotic state subjects may show increased power of perception, and are strangely susceptible to suggestions or guidance by the experimenter. In a second attack the patient often refers back to the first, and does things in continuation or repetition of what he previously did, apparently taking up the same line of thought and action. The morbid states, long or short, are joined together by memory, but are wholly unknown in the normally conscious states. In other words, the patient leads two (or three, according to a few observations) separate lives, each one forming a chain of interrupted conscious states. In epilepsy we observe remarkable breaks in normal consciousness: the patient goes through certain acts or walks a distance or commits a crime in a dream-like state, and suddenly, after the lapse of a few minutes, hours, or days, becomes normally conscious and has no recollection of what he did with such apparent system and purpose during the seizure. It might, perhaps, be as well to classify these phenomena under the head of amnesia. A case is on record where a man travelled, seeming normal to fellow-travellers, from Paris to India, and who was immensely astonished on coming to himself (return to common consciousness) in Calcutta. Many murders have been committed with apparent design and with skill by epileptics, who upon awaking from their dream-like state were inexpressibly horrified to hear of their misdeeds.