52 A COURSE ON ZOOLOGY. 



abdomen, and may be considered as the centre of the 

 sympathetic system. It has even been called the ab- 

 dominal brain. 



Functions of the Nervous System. The nervous sys- 

 tem is the seat of sensation, of intellectual perception, 

 and of voluntary and involuntary motion ; at the same 

 time it presides over the acts of nutrition and secretion, 

 and regulates the whole economy. 



It is easy to prove the universal influence of this sys- 

 tem. Whenever nerve-action is arrested the function of 

 the part is interrupted, and all manifestations of life are 

 destroyed. If the nerve supplying the kidneys be cut, 

 those organs immediately cease to produce their ordinary 

 excretion ; if the nerve distributed to any member be cut, 

 the member at once loses all sensation, all possibility of 

 motion. This is a law to which there is no exception. 



Each of the different parts of the nervous system has 

 its own particular work to do. Nutrition, sensation, and 

 movement are not under the influence of the same nerve- 

 centres. 



Nutrition is, to a great extent, under the supervision 

 of the great sympathetic, and for this reason the name 

 nervous system of organic life has been sometimes applied 

 to the sympathetic system. On the other hand, sensa- 

 tion and movement are under the control of the cerebro- 

 spinal system. If, as is the case, ramifications of both 

 systems are found distributed all over the body, it is 

 because all our organs must live and be nourished, and 

 to a certain extent all are endowed with sensation and 

 movement. 



To understand the operations of the nervous system, 

 it must be remembered that the nerves have no other 

 function than to establish communication between the 



