DIVISIONS OF THE NERVOUS SYSTEM. 259 



the explanation of action. Yet even now a few leading facts have been 

 determined, which foreshadow the attitude in which the whole subject 

 will stand when it comes to be better understood. Among these may 

 be numbered the localization of special functions in special parts of the 

 nervous centres, as was observed by Gall ; the double office of the spinal 

 nerves, first recognized by Bell, that their anterior roots are motor and 

 posterior sensory ; the conversion of impressions made at the periphery 

 into motions, reflex action, as it has been termed, first clearly recognized 

 by Hall ; the relation of the ganglia at the base of the brain to the cere- 

 brum and the spinal cord, as shown by Carpenter ; and particularly the 

 general condition on which the activity of the entire system depends, 

 that it undergoes oxidation or waste, and, among other products, gives 

 origin to salts of phosphoric acid. 



For the sake of convenience of description, the nervous system is usu- 

 ally regarded as consisting of two portions, the cerebro-spi- Di v i s i on O f t h e 

 nal and sympathetic. The former is composed of the spi- nervous system 

 nal cord, the brain, the nerves proceeding from them, and S p ma i &ri ~ 

 their ganglia; the sympathetic is composed of a series of sympathetic, 

 ganglia, united by intercommunicating threads on each side of the ver- 

 tebral column, and supplying branches to the coats of the blood-vessels 

 and viscera of the great cavities. Both portions contain two kinds of 

 structure, a fibrous and a vesicular. The latter is found in _.. 



\ f Fibrous and 



various situations ; the former serves to connect those mass- vesicular stmc- 

 es with one another, or to furnish means of communication *' 

 from point to point ; the office of the ganglia, or nervous centres, is for 

 the reception of impressions and the origination of motions. In the 

 brain the impressions of external circumstances are, as it were, registered, 

 and from it originate the processes of intellection. 



The study of this portion of the mechanism of man brings us therefore 

 in contact with metaphysical science, and some of its funda- Connection of 

 mental dogmas we have to consider. Nearly all philoso- metaphysical 

 phers who have cultivated, in recent times, that branch of phl1 

 knowledge, have viewed with apprehension the rapid advances of physi- 

 ology, foreseeing that it would attempt the final solution of problems 

 which have exercised the ingenuity of the last twenty centuries. In 

 this they are not mistaken. Certainly it is desirable that some new 

 method should be introduced, which may give point and precision to 

 whatever metaphysical truths exist, and enable us to distinguish, sepa- 

 rate, and dismiss what are only vain and empty speculations. 



So far from philosophy being a forbidden domain to the physiologist, 

 it may be asserted that the time has now come when no one is entitled 

 to express an opinion in philosophy, except he has first studied physiol- 

 ogy. It has hitherto been to the detriment of truth that these processes 



