476 OF THE NERVOUS SYSTEM AND ITS ACTIONS. 



however, that every movement which takes place in the Animal body is 

 dependent upon the Nervous System ; for we have seen that the Muscu- 

 lar tissue may be employed to perform contractions excited by stimuli 

 applied to itself, and that it may thus execute a set of movements in 

 which the nervous system has no direct participation. And it is desirable 

 that the Student should observe, that these are, in all instances, those 

 most directly connected with the Vegetative functions, and, at the same 

 time, those of the simplest and most straightforward character. Thus, 

 the peristaltic movement, by which the alimentary and faecal matters 

 are propelled along the Intestinal tube, results from the direct excite- 

 ment of the contractility of its muscular walls, and is entirely indepen- 

 dent of Nervous agency ; and this movement is accomplished by the 

 successive contraction of the different fasciculi surrounding the tube, 

 which take up (as it were) each others' action ( 352). So again, 'the 

 successive contractions and dilatations of the cavities of the Heart, 

 which perform so important a part in the Circulation of the blood, are 

 the result of the properties inherent in that organ ; the muscular fibres 

 of which are excited to a peculiar rhythmical and consentaneous con- 

 traction, by the flow of blood into the cavities when dilating. More- 

 over, in the Excretory ducts of various glands, we find a Muscular coat, 

 by which the fluids secreted in the glands are propelled towards their 

 outlet on the exterior of the body, or on one of its free internal surfaces. 



843. In these instances, then, we observe that. the simple Contractility 

 of Muscular structure, excited by direct stimulation, is applied to effect 

 the movements most closely connected with the Organic functions. With 

 the processes, therefore, which take place in the penetralia af the system, 

 the Nervous System has no direct concern. Its office is to guard the 

 portals for entrance and exit ; and to fill those chambers, which admit 

 the new materials from the external world ; or to empty the receptacles, 

 which collect from the interior of the system the effete matters that are 

 to be cast out from it. And we find that, for these oflices, the Nervous 

 system is employed in its very simplest mode of operation ; that which 

 does not involve Sensation, Intelligence, Will, or even Instinct (in the 

 proper sense of that term), but which may take place independently of 

 all consciousness, by the simple reflexion of an impression, conveyed 

 to a ganglionic centre by one set of fibres proceeding towards it from 

 the circumference, along another set which passes from it to the mus- 

 cles, and calls them into operation ( 394). This reflex function, there- 

 fore, is the simplest application of the Nervous System in the Animal 

 body. We shall presently see reason to believe, that a very large pro- 

 portion of the movements of many of the lower animals are of this reflex 

 character ; and that they are not necessarily accompanied by sensation, 

 although this may usually be aroused by the same cause which produces 

 them. As we rise, however, in the scale of Animal existence, we find 

 the reflex movements forming a smaller and smaller proportion of the 

 whole ; until, in Man, they constitute so limited a part of the entire 

 series of movements of which the Nervous system is the agent, that their 

 very existence has been overlooked. 



844. But the main purpose of the Nervous System is to serve as the 





