348 GENERAL PURPOSES OF NERVOUS SYSTEM. 



greater complexity of structure, and obviously acquiring 

 higher and yet higher ' functions ; so that in Vertebrated 

 animals, and more especially in Man, it is evidently that 

 portion of the organism to whose welfare everything else is 

 brought*into subordination ( 73). And we observe this to be 

 the case, not merely in virtue of its direct instrumentality as 

 the organ of Mind, but also in the intimacy of its relation to 

 the Organic functions, which are placed in great degree under 

 its control. Thus we find that the inlets and outlets to the 

 Digestive apparatus, the mechanism by which food is brought 

 to the mouth and conveyed into the stomach, and that by 

 which indigestible matters are voided from the large in- 

 testine, are subjected to its influence ; although the act of 

 digestion itself, and the passage of the aliment from one end 

 of the canal to the other, are performed independently of it. 

 So, again, the movements of Eespiration, by which the air 

 within the lungs is renewed as fast as it becomes vitiated, are 

 not only effected through its instrumentality, but are placed, 

 for the purposes of Vocalization, as far under the control of 

 the Will as would be consistent with a due regard to the 

 safety of life. Yet among many of the lower tribes of Animals, 

 the ingestion of food and the aeration of the circulating fluid 

 are provided-for by ciliary action alone ( 45), in which we 

 have every reason to believe that nervous agency has no par- 

 ticipation whatever. 



430. If, taking the Nervous System of Man as the highest 

 type of this apparatus, we analyse in a general' way the actions 

 to which it is subservient, we find that they may be arranged 

 under several distinct groups, which it is very important to 

 consider apart, whether we are studying his psychical J functions 

 or those of the lower animals. 1. The simplest mode of its 

 action is that in which an impression made upon an afferent 

 nerve excites, through the ganglionic centre in which it ter- 

 minates, an impulse in the motor nerve issuing from it, which, 

 being transmitted by it to the muscular apparatus, calls forth 

 a respondent movement. Of this action, which is called reflex, 

 or " excito-motor," and which may be performed without any 

 consciousness either of the impression or of the motion, we 

 have already seen examples in the movements of Deglutition 



1 This term is used to designate the sensorial and mental endowmenti 

 of Animals, in the most comprehensive sense. 



