200 THE HUMAN BOD T. 



forms a uniting anatomical and physiological bond through 

 the agency of which unity and order are produced in the 

 activities of different and distant parts. We may compare 

 it to the Western Union Telegraph, the head office of 

 which in New York would represent the brain and spinal 

 cord; the more important central offices in other large 

 cities, the sympathetic ganglia; and the minor offices in 

 country stations the sporadic ganglia; while the tele- 

 graph-wires, directly or indirectly uniting all, would corre- 

 spond to the nerve-trunks. Just as information started along 

 some outlying wire may be transmitted to a central office, 

 and from it to others, and then, according to what happens, 

 to it in the centre, be stopped there, or spread in all c>irec- 

 tions, or in one or two only, so may a nervous disturbance 

 reaching a centre by one nerve-trunk merely excite changes 

 in it or be radiated from it through other trunks more 

 or less widely over the Body and arouse various activi- 

 ties in its other component tissues. In common life the 

 very frequency of this uniting activity of the nervous sys- 

 tem is such that we are apt to entirely overlook it. We 

 do not wonder how the sight of pleasant food will make the 

 mouth water and the hand reach out for it; it seems as we 

 say " natural" and to need no explanation. But the eye 

 itself can excite no desire, cause the secretion of no saliva, 

 and the movement of no limb. The whole complex result 

 depends on the fact that the eye is united by the optic, 

 nerve with the brain, and that again by other nerves with 

 saliva-forming cells, and with muscular fibres of the arm; 

 and through these a change excited by light falling inta 

 the eye is enabled to produce changes in far removed or- 

 gans and excite desire, secretion and movement. In cases- 

 of disease this action exerted at a distance is more apt to ex- 

 cite our attention : vomiting is a very common symptom of 

 certain brain diseases and most people know that a disor- 

 dered stomach will produce a headache ; while the pain 

 consequent upon the hip-disease of children is usually felt, 

 not at the hip-joint bnt at the knee. 



