138 FUNCTIONS OF THE NERVOUS SYSTEM. 



within reach of these, a muscular apparatus is provided, by which any thing 

 that comes within its grasp is conveyed downwards, through a reflex opera- 

 tion, originating in the impression made upon the surface of the pharynx. 

 Now this action, in the ordinary condition, may be considered as attended with 

 sensation, in order that the Animal may be called upon to execute those other 

 movements which will bring food within the reach of the apparatus of deglu- 

 tition. The Polype is dependent for its supplies of aliment upon what the 

 currents in the surrounding fluid, or other chances, bring into its neighbour- 

 hood ; but any thing which touches its tentacula is entrapped and conveyed 

 into its stomach. The anencephalous Infant, again, can swallow, and even 

 suck ; but it can execute no other movements adapted to obtain the supply of 

 food continually necessary for maintenance, because it has not a mind which 

 sensations could awake into activity. 



182. The sensation connected with reflex actions has not only this important 

 end, but it frequently contributes to enjoyment, as in suction and ejaculatio 

 seminis. Now there is evidence that the latter of these processes, involving 

 though it does the combined action of a number of muscles, and dependent as 

 it seems upon sensation of a very peculiar kind, may take place without con- 

 sciousness on the part of the individual. Brachet mentions a case of this kind 

 in the Human subject, in which the patient's own testimony could be adduced ; 

 and he ascertained that emission could be produced in dogs, in which the 

 spinal cord had been divided in the back, and in which, therefore, it can 

 scarcely be doubted that the sensibility of the genital organs was destroyed. 

 Such cases, it might be thought, are sufficient to prove that the Reflex power, 

 operating independently of sensation, is not confined to such irregular con- 

 vulsive movements as are seen in Man after disease or injury ; but is exer- 

 cised in producing the regular combined actions which are necessary for the 

 maintenance of the organic functions. The sensation accompanying these 

 actions, moreover, frequently affords premonition of danger, or gives excite- 

 ment to supplementary actions destined to remove it, as in the case of respira- 

 tion ; for where any thing interferes with the due discharge of the function, 

 the uneasy sensation that ensues occasions unwonted movements, which are 

 more or less adapted to remove the impediment, in proportion as they are 

 guided by judgment as well as by consciousness. Again, sensation often 

 gives warning against inconvenience, as in the excretory functions ; and here 

 it is very evident, that its object is not only (if it be at all) to excite the asso- 

 ciated muscles necessary for the excretion, but actually to make the will set 

 up the antagonizing action of the sphincters, as will be hereafter explained 

 ( 202). There is one unequivocal case, in the ordinary condition of the 

 human body, of reflex action without sensation ; this is the muscular contrac- 

 tion, by which the food is propelled from the bottom of the pharynx to the 

 stomach. Unless the morsel be very bulky, so as to press on the surrounding 

 parts, or be very different in temperature from the surface it touches, or have 

 any peculiar irritating quality, we are not more conscious of its presence, 

 whilst it is passing down the lower part of the ossophagus, than when it is 

 being propelled along the intestinal tube ; and yet, as Dr. J. Reid's experi- 

 ments* have shown, this contraction is of a reflex character, not being stimu- 

 lated by direct contact, but requiring the completeness of the nervous circle 

 for its performance. 



183. We shall now separately consider the chief operations, in which the 

 Spinal Cord and its system of nerves are usually concerned, in the ordinary 

 course of the vital actions of the Human body. Upon taking a general survey 

 of these, it will be found that their ordinary function is, to supply the condi- 



* Edinb. Med. and Surg. Journ, vol. xlix. 



