492 MATER i A MEDIC A AND THERAPEUTICS. 



CHAPTER XII. 



THE NERVOUS SYSTEM. 



THE therapeutical relations of the nervous system are as 

 extensive as those of the whole body itself. Pain, for example, 

 is constantly associated with local disease, and many of the 

 most distressing diseases of the viscera are disturbances of 

 nervous mechanisms. Here we must confine ourselves chiefly 

 to the therapeutical relations of the higher nervous centres, 

 representing sensation, consciousness, and voluntary motion, 

 especially to the means by which we may relieve pain in 

 general, produce unconsciousness, and induce sleep. The 

 student must also clearly understand that we are approaching 

 the therapeutics of the nervous system from the physiological 

 side, i.e. the treatment of symptoms only. The treatment 

 of the pathological processes, such as haemorrhage, degeneration, 

 syphilis, which constitute these diseases and cause these 

 symptoms, is another "and even more important part of the 

 management of this class of cases, and one which falls under 

 other heads. 



I. PHYSIOLOGICAL RELATIONS. 



Nervous tissue is a kind of protoplasm with highly special- 

 ised properties, which may be resolved into the one great 

 property of displaying or discharging force when brought into 

 contact with certain influences. "We name this property 

 irritability ; the influence which calls it forth, an irritant ; the 

 act of calling it forth, irritation. If the effect be the display of 

 more force than ordinary, we speak of the influence as a 

 stimulant, and of the act or result as stimulation. If the effect 

 of irritation be the display of less force than ordinary, we say 

 there has been depression that the influence is a depressant. 

 Much discussion is still going on as to the nature of irritation, 

 stimulation, and depression, but the points just indicated are 

 clear enough for our present purpose. 



Plan of the Nervous System. The nervous system, though 

 forming one continuous mass of nervous tissue, is built up of a 

 number of centres, which are connected with an irritable surface, 

 and with the organs of force. An impression made on the sur- 

 face by an irritant is conveyed by an afferent nerve, or tract, to 

 the centre ; effects there some change upon the protoplasm ; and 

 either remains as potential energy, or flows out again through 

 efferent tracts and nerves, as an impulse, to the organs of force 

 the muscles, glands, vessels, etc. This process is spoken of as 

 reflex action. Nervous substance is, however, not simply 



