502 MATERIA MEDIC A AND THERAPEUTICS. 



treatment ; very frequently disturbed ; sometimes excessive. 

 Pain is the common cause of insomnia, but sleep may be pre- 

 vented 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 encourage- 

 ment 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, anaes- 

 thesia, and disturbances of consciousness and of the mind gene- 

 rally, 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, 



