246 FUNCTIONS OF THE NERVOUS SYSTEM. 



exciting them to contraction. There is reason to believe, however, that this 

 motor impulse may proceed from at least two distinct sources; being either 

 the direct consequence of the sensation, acting involuntarily as an emotional 

 or instinctive impulse ; or resulting from a more or less complicated series 

 of intellectual operations, which terminate in an act of volition or will. To 

 these functions, taken collectively, the Encephalon, and the nerves connected 

 with it, are alone subservient ; and we may probably assign the group of sim- 

 ple consensual or involuntary actions to the ganglia which receive the nerv- 

 ous trunks from the organs of sense, and which make up nearly the whole 

 of the Cephalic masses of ganglia in the Invertebrata ; whilst the Cerebral 

 hemispheres of Vertebrata are the instruments of the intellectual operations 

 and of the mandates of the will. 



ii. Certain parts of the Nervous System receive impressions which are 

 propagated along afferent fibres, that terminate in ganglionic centres distinct 

 from the sensorium; and in these a reflex motor impulse is excited, which, 

 being conveyed along the efferent trunks proceeding from them, excites mus- 

 cular contraction, without any necessary intervention of sensation or volition. 

 Of this function (called by Dr. Hall, to whom the discovery of it is in a great 

 part due, the reflex function), we shall find that the portion of the Spinal 

 Cord of Vertebrata, which is not continuous with the fibrous structure of the 

 brain, together with the portion of the nervous trunks which are connected 

 with it alone, is the instrument : whilst, in the Invertebrata, the same office 

 is performed by ganglia still more obviously disconnected from the cephalic 

 mass. 



in. Another division of the Nervous System appears to have for its object, 

 to combine and harmonize the muscular movements immediately connected 

 with the maintenance of Organic life ; and to bring these into relation with 

 certain conditions of the mind. There is reason to believe (though this is 

 less certain) that it also influences, and brings into connection with each other, 

 the processes of Nutrition. Secretion, &c. ; though these, like the muscular 

 movements just mentioned, are essentially independent of it. This portion 

 of the nervous apparatus is commonly known under the name of the Sympa- 

 thetic system. 



308. Now, in reference to the first of these classes of operations, it is well 

 to explain that though the Physiologist speaks of the intellectual powers, 

 moral feelings, &c., as functions of the Nervous System, they are not so in 

 the sense in which the term is employed in regard to other operations of the 

 bodily frame. In general, by the function of an organ, we understand some 

 change which may be made evident to the senses ; as well in our own sys- 

 tem, as in the body of another. Sensation, Thought, Emotion, and Volition, 

 however, are changes imperceptible to our senses, by any means of observa- 

 tion we at present possess. We are cognizant of them in ourselves, without 

 the intervention of those processes by which we observe material changes 

 external to our minds ; but we judge of them in others, only by inferences 

 founded on the actions to which they give rise, when compared with our own. 

 When we speak of sensation, thought, emotion or volition, therefore, as func- 

 tions of the Nervous System, we mean only that this system furnishes the 

 conditions under which they take place in the living body ; and we leave the 

 question entirely open, whether the "^vxn has or has not an existence independ- 

 ent of that of the material organism, by which it operates in Man, as he is 

 at present constituted. 



309. In regard to the second class of actions, it may be remarked, that they 

 are nearly all connected, more or less closely, with the maintenance of the 

 Organic junctions, or with the protection of the body from danger. Thus 

 the movements of the pharynx supply to the stomach the alimentary materi- 



