The action of narcotics is very complex, extending from one extremity of the sensory side of the nervous system to the other, influencing also its motor side, and disturbing the sensory, motor, and metabolic functions of most of the viscera. In a person under the full influence of Opium, an impression can only be made with difficulty upon the peripheral nerves, or on the organs of sense; it is slowly and imperfectly conducted; and it is imperfectly perceived in the cerebrum. Thus cut off from all but the most powerful external impressions, and itself reduced in activity, the cerebrum is practically in the condition of deep sleep, characterised by unconsciousness. A fact of much greater importance, since unconsciousness is not of itself serious, however prolonged, is that it is accompanied by great depression of the medulla, that is, of the respiration and circulation, which, although sometimes to be turned to useful account, may readily prove injurious or even highly dangerous. We thus possess in narcotics a powerful means (1) of arresting perception, (2) of inducing sleep, and (3) of soothing the great vital functions, all of which may be of the greatest therapeutical service. 4. Sleep.-We possess many methods of promoting or producing sleep, which we call hypnotics ( sleep), or less properly "narcotics." Thus we may be able to secure mental calm, or the absence of noise and light, and to prevent or relieve pain or other disturbing impressions, such as attend indigestion, heart disease, and cough. Along with these indirect hypnotics, we may employ direct hypnotics, which act on the convolutions, either through the circulation or immediately upon the cells, in either way reducing nervous metabolism. Amongst medicinal hypnotics, the purest are perhaps the Bromides, which appear to bring the brain into a condition which favours the advent of natural sleep, rather than to induce it artificially, if any such distinction can be drawn. Artificial sleep is readily induced by the narcotics proper, including Chloral, Opium, and Alcohol, as well as general anaesthetics, all of which produce hypnotism amongst their other effects, and may be used for this purpose.

III. Pathological Relations

We will now briefly consider some of the most common and typical disturbances of the nervous system. The organic diseases of this system are of great variety, including morbid states of the vessels, syphilis, degenerations, etc., but it is only the principal symptoms to which they give rise that will be noticed here for the purpose of illustrating the applications of the measures just discussed.

1. Disturbances of Sensation : Pain.-Pain is a familiar disturbance of common sensibility of a peculiarly distressing kind. As an expression of disease, whatever the tissue affected, pain always originates in some nervous structure between and including the periphery and the convolutions, but in every instance it is referred to the periphery. When pain is severe, it is accompanied by certain other phenomena, such as mental depression and restlessness, sleeplessness, weakening of the heart, indigestion, and other visceral disturbances. These may be in part effects of the morbid condition on which the pain also depends, but it is to be observed that pain is in itself a powerful depressant of the centres and viscera, just like local depressants of a pharmacodynamical nature.

2. Paralysis

Paralysis. Loss of power, may be taken as an instructive illustration of motor disturbance. Comparably with pain, paralysis depends on injury or disease, of whatever nature, in some part of the motor side of the nervous system-the convolutions, basal ganglia, medulla, lateral column and other motor tracts, the anterior root of the spinal nerve, the nerve trunk, or the terminal motor apparatus in the muscle; occasionally it is distinctly a reflex effect of sensory disturbance; but the paralysis is always seen in the muscle. No class of disease teaches us more clearly the dependence of rational therapeutics upon an accurate knowledge of the anatomy, physiology, and pathology of the parts affected.

3. Side by side with pain and paralysis respectively, there are to be ranged many allied conditions. Thus, allied to pain, and depending like it on disturbance of some part of the sensory tract, are the sensations of numbness, coldness, excessive sensibility to touch (hyperaesthesia), excessive sensibility to painful impressions, such as pin-prick (hyperalgesia), and the various disturbances of the special senses; loss of the sense of touch (anaesthesia), loss of the sense of pain (analgesia), and alteration or loss of the organic sensations relating to the stomach, bowels, heart, bladder, etc. In the same way we place beside paralysis other motor disturbances, whether in the form of increased muscular movements-chorea (St. Vitus's dance), tremors, spasms, convulsions, or disturbed movements of the viscera, as of the heart, intestines, uterus, vessel walls, etc.; and we say that they may be due to disease of any part of the motor tract from one extremity to the other, or of some part of the sensory area of the nervous system by reflection through the centres. Reflex spasms, convulsions, and visceral disorders, are especially common.

4. Disturbances of consciousness, and of the other higher faculties of the nervous system, include unconsciousness or insensibility, delirium or excitement, and the great class of "diseases of the mind" constituting insanity. Unconsciousness may be the result of injuries to the head; of interference with the blood-supply to the brain, familiarly seen in fainting; of interference with the supply of air to the brain, as in asphyxia; or of poisons, such as alcohol and opium. To these causes we may add organic diseases of the brain, and indeed most diseases just before death. Delirium and other forms of excitement are phenomena of many diseases, and of the action of a variety of poisons, and must be regarded as associated, both as effects and causes, with excessive nervous metabolism, leading rapidly to exhaustion.