5. Sleep is most commonly deficient or absent when it calls for treatment; very frequently disturbed; sometimes excessive. Pain is the common cause of insomnia, but sleep may be prevented or broken by cerebral exhaustion (? vascular paralysis) from overwork, by mental anxiety or distress, by oppressed or breathless feelings in the chest, by dyspeptic troubles, and by other distressing sensations, such as irritability of the bladder, spasms of the muscles, and itching of the skin. Sometimes sleeplessness appears to be idiopathic, i.e. a disorder per se. Excessive sleepiness, or continual tendency to sleep, is a result of the retention and circulation in the system of urea or allied products which have not been sufficiently excreted by diseased kidneys; and drowsiness, to a less degree, is a frequent symptom of anaemia, or of disturbed metabolism in the liver, as we saw in the tenth and eleventh chapters. Certain articles of diet, especially alcohol in the form of beer, produce the same effect.

IV. Natural Recovery

As the nervous system is the most impressionable of all the tissues, so it seems to possess the power of recovery most quickly and most perfectly from conditions of disorder, when the causes of these-are removed. Thus, pain may instantly disappear upon a slight change of temperature, on the application of a weak electrical current, with the alteration of the chemical reaction of the part, or in consequence of the contact with it of a minute quantity of some drug-any of which means will have sufficiently restored its normal condition, or counteracted the abnormal state which gave rise to the distress. In no department of pathology, therefore, is the indication clearer, and encouragement greater, to step in and assist nature by pharmacodynamical measures. Unfortunately, here, as elsewhere, there are certain limits to treatment. The disorders of the nervous system to which we have alluded, such as paralysis, spasm, pain, anaesthesia, and disturbances of consciousness and of the mind, generally, are too often but the phenomena or symptoms of organic disease of the delicate nervous structures. Scarcely less hopeless is the prospect of curing certain functional disorders of the nervous system, without discoverable anatomical cause, such as epilepsy and hysteria. But even in both these classes of cases, many of the most urgent symptoms, and the severity and frequency of others, can be mitigated by the measures which we have just reviewed, as we shall now attempt to show.

V. Therapeutics

In drawing a rational conclusion from what we have studied under the four preceding heads, we approach, as we proposed, the consideration of the therapeutics of the nervous system chiefly from the point of view of symptoms.

1. Disturbances of Sensation: Pain, and the use of Anodynes.-Our review of the physiological and pathological relations of pain leads us to its rational treatment. We must discover, first, its morbid cause, and secondly its exact physiological significance, and apply our measures accordingly.

The scientific use of anodynes, as we have already suggested, is founded upon correct diagnosis. It will frequently he found that when the cause is known, pain can be removed without the employment of any nervine remedy, and in every instance this treatment should be entertained or attempted. An abscess will be relieved by the knife, headache by purgation, syphilitic periostitis by Iodides. We thus discover a great group of measures which, whilst they are not anaesthetics, are indirect anodynes, because they attack the pathological cause of the pain, and do not immediately act upon nervous tissue. For practical purposes, anodynes may be classified into (1) indirect anodynes; (2) direct anodynes which act on the peripheral nerves only; and (3) direct anodynes which act on the centres as well as the periphery. In many instances these may be combined.

a. Indirect anodynes are necessarily a heterogeneous group, and include surgical operations of every kind, which are amongst the readiest and most radical of all, e.g. opening abscesses, simple physical protectives, such as ointments and oils in burns; poultices and warm fomentations, and cold in various forms.

Local irritants, such as mustard and blistering agents, which cause much pain at first, may become local anodynes by producing an effect which is called counter-irritation. We shall discuss fully this class of remedies in chapter xv (. Therapeutical Processes Connected With The Surface Of The Body)., but we 'may for the present refer their action to exhaustion of the irritability and conductivity of the local nerves, to dilatation of the vessels and relief of anaemia, and to some influence on the nervous centres corresponding to the affected part. Another powerful natural group of local anodynes, which are chiefly indirect, but partly also direct, in their action, consists of the essential oils, such as Turpentine, Camphor, and the Oils of Cloves, Mint, etc. These have a complex action: they destroy the organisms of disease by virtue of being antiseptic; they dilate the vessels, causing redness and heat; and they depress the peripheral nerves after temporary pain. Certain allied artificial products possess a similar indirect and direct anodyne power, e.g. Carbolic Acid and Creasote. Besides these local indirect anodynes, we possess an unlimited number which act generally: as many, indeed, as the remediable causes of pain. Thus, headaches may be relieved, under different circumstances, by any of the local measures just enumerated, or by such diverse general remedies as purgatives, Quinia, Iron, Iodides, and Alcohol, quite independently of the direct anodynes which we may consider it necessary to apply.

b. Local Anodynes.-When treatment directed to the cause of the pain fails or is insufficient, we must next attempt to reduce the irritability of the nerves by local means. Direct local anodynes may now be rationally employed. Thus in neuralgia, constitutional treatment must be combined with the application of a local anodyne sufficiently powerful to interfere with the reception and conduction of impressions. We therefore employ Aconite, Belladonna, Opium, the confined vapour of Chloroform, Alcohol, or Ether, the Volatile Oils, Carbolic Acid, Creasote, heat (which must often be extreme), extreme cold, the continuous current, or local nervous irritants. Most of the drugs mentioned are applied in the form of liniments, lotions, or ointments. Opium may be administered by the endermic or hypodermic method, the former being now almost entirely superseded by the latter, which is by far the most valuable of all anodyne measures, from the readiness with which it can be given, and the rapidity and completeness of its action. Alcohol or Chloroform may be poured on lint, and evaporation prevented, or rubbed on the part and covered.