220 THE NERVOUS SYSTEM 



21. What sort of change takes place in the nervous tissue 

 when its excitability is aroused, is not known ; certainly none 

 is visible. On this account, it has been thought by some that 

 the nerve-fibre acts after the manner of a telegraph wire ; that 

 is, it transmits its messages without undergoing any material 

 change of form. But though the comparison is a convenient 

 one, it is far from being strictly applicable, and the notion 

 that nerve-force is identical with electricity has been fully 

 proved to be incorrect. 



22. The Functions of the Nerves. The nerves are the in- 

 struments of the two grand functions of the nervous system 

 Sensation and Motion. They are not the true centres of either 

 function, but they are the conductors of influences which occa- 

 sion both. If the nerve in a limb of a- living animal be laid 

 bare, and irritated by pinching, galvanizing, or the like, two 

 results follow, namely: the animal experiences a sensation, 

 that of pain, in the part in which the nerve is distributed, and 

 the limb is thrown into convulsive action. When a nerve in a 

 human body is cut by accident, or destroyed by disease, the 

 part in which it ramifies loses both sensation and power of 

 motion; or, in other words, it is paralyzed. We accordingly 

 say that the nerves have a two-fold use a sensory and a 

 motor function. 



tion of little brains, if I may use a rather crude expression. It is, as the 

 Swiss would say, the 'great council' of this federative republic, which 

 counterpoises that cerebral royalty within us. It has been well named 

 the great sympathetic nerve, and this it is which makes the laws by 

 which our interior life is governed. The nutritive apparatus of a country, 

 its commerce, its industry, the incessant labor of its citizens, by which 

 the public wealth is built up and also let us add, the throbs of the 

 national heart all this the sympathetic system full plainly shows us 

 should be left to itself. It w.ould be a fine affair if the brain had to 

 watch over the service of the stomach, or if, at its convenience, it regu- 

 lated the movements of the master who disposes of its life. Besides, 

 what would become of the poor body if the least drowsiness attacked the 

 universal centre ? Happy it is for us and let us not be slow to own it 

 that nature has armed herself against these encroachments of power." 

 Mace's The Little Kingdom. 



21. Change in the nervous tissues ? Nerve force and electricity ? 



22. Functions of the nerves? In the case of the nerve of a living animal? Of the 

 human body ? 



