like slumber of the body while the mind remains awake. The sleep from the action of excessive cold, which precedes death, is due, of course, to general retardation of the circulation, which in due time affects the brain, but probably has but a partial analogy with natural sleep. It has not been sufficiently examined to determine whether dreams accompany it at any stage. The delusions from the abuse of opiates and those of delirium tremens are of the class of waking dreams. Death by drowning is asserted to be preceded by extraordinary waking dreams, sometimes rather pleasurable than otherwise.
The most important of all species of sleep for our present purposes of comparison are those produced by anæsthetic agents. The general use of these is now but about half a century old, though it has been shown that the principle of anæsthesia and its use in surgery, etc., is about as old as the Christian era. Dioscorides describes the use of the mandragora root, steeped in wine, as an anaæthetic drink to produce a sleep in which painless amputations and other surgical operations could be effected, Pliny and Apuleius (author of the famous Golden Ass) each make similar statements. Sir B. W. Richardson announced, in 1875, that he had experimented with mandragora, and had largely confirmed the ancient stories about it. The moderns have a great number of anæsthetic agents, some of which are permanent gases, others volatile liquids, which are mostly administered by inhalation; but we yet know very little, in exact scientific detail, about most of them. Some, when given in properly graduated doses, furnish us with conditions approaching closely to those of natural sleep, generally of a dreamless kind; but others, if given in small doses, furnish us examples of sleep of the will power and reasoning functions, accompanied by emotional dreams and hallucinations. In the case of nitrous oxide (laughing gas), especially when given in moderate doses, mixed with air ox oxygen, emotional excitements of the most remarkable kind result. The subject will often fly into an energetic rage, manifesting a violent and ludicrous pugnacity toward those about him. Others will declaim in an oratorical manner, sometimes sensibly and coherently. Of such occurrences the subject often retains vague memories, like those of natural dreams. Thus memory persists during the action of this agent, as in true sleep; and, as in sleep, the will-control is wanting. The natural instincts, no longer restrained, rise up and assert themselves. "In vino Veritas." Ordinary alcoholic intoxication, indeed, is but one kind of anæsthesia, and passes in its progress through the same characteristic stages or phases that have been previously defined.
The generalization remaining to be brought forward is as follows: It has already been indicated that of all the known arti-
