cHAr. IX.] NERVOUS SYSTEM AND ORGANS OF SENSE. 253 



nervous system, and tliis reciprocal activity is mainly eflfected with- 

 out " feeling" coming into play. 



Thus the nervous system may be defined as the great co- 

 ordinating SYSTEM of the body ; co-ordinating the action of the 

 parts of the body one with another, co-ordinating the action of such 

 parts with relation to surrounding influences and conditions, and 

 also co-ordinating the action of the body as a whole with relation 

 to such influences and conditions — the activity of the nervous system 

 being more or less frequently accompanied by acts of sensation. 



§ 2. Sensation is incapable of definition, since to be understood 

 it must be experienced, and every man must know what it is to have 

 a feeling who knows anything whatever, as "sensations" are with 

 us the indispensable antecedents of ideas, and therefore of all know- 

 ledge. Sensation, however, may be described as a special and alto- 

 gether peculiar vital organic activity, which accompanies certain 

 actions of the nervous system occurring under the requisite con- 

 ditions. 



§ 3. That system of parts, the nervous system, the nature of 

 which has just been defined, is made up, like the skeleton, of two 

 great divisions, one axial, the other peripheral. Besides these, that 

 part of the peripheral system which especially supplies the viscera, is 

 commonly reckoned as distinct, under the name of the sympathetic 

 system. The whole consists of a peculiar tissue (to be shortly 

 described), forming a white or grey pulpy mass in the form of bulky 

 aggregations, and of cords or threads, which radiate in all directions 

 from such aggregations. 



The a.vial part of the nervous system is that bulky aggregation 

 of nervous or neural matter, which occupies the cranial cavity and 

 the neural canal of the vertebral column (Fig. 2, n), that is to say, 

 it is the brain and spinal cord which are together spoken of as the 

 cerebrospinal axis. 



The peripheral part of the nervous system is that system of cords 

 or threads of neural matter which are called nerves, and which 

 proceed out from the cerebro-spinal axis to all parts of the body. 

 Scattered amongst them every here and there are certain aggrega- 

 tions of nervous matter — In rounded or irregularly- shaped masses 

 of various sizes — called ganglia. That portion of the peripheral 

 part of the nervous system called the sympatJictic (and which, as 

 just observed, is specially distributed to the viscera) difi'ers somewhat 

 from the rest as to its minute structure. 



§ 4. Nervous TISSUE is a soft, nitrogenous substance of very com- 

 plex chemical composition. It is reducible into water, albuminoid 

 matter, fatty and extractive matters, and sundry salts. Different parts 

 of it contain from 73 to 85 per cent, of water, 7 to 10 per cent, of 

 albuminoid matter, and from 5 to 15 per cent, of fat. 



The fatty matters consist of cerebric, glycero-phosphorlc, and 

 palmitic acids, with olein, margarin, pal mi tin, and cholesterin. 

 From brain-ash the following percentage of different substances 

 has been obtained. Phosphate of potash, 55*24 ; phosphate of soda, 



