REFLEX ACTIONS OF THE SPINAL CORD. 379 



of the limbs may be kept-up by reflex action, while their 

 general direction is guided by visual sensation ( 479). ^And 

 even when the mind is sufficiently on the alert to guide, direct, 

 and control the motions of the limbs, their separate actions 

 appear to be performed without any immediate exertion of the 

 will ; and probably depend, therefore, rather upon the reflex 

 function of the spinal cord, than upon the continual influence 

 of the brain. 



472. Besides the reflex movements of deglutition and re- 

 spiration, which have been formerly considered ( 195 and 

 340), and those of locomotion, on which we have now dwelt 

 sufficiently, there are several others of a similar character, all 

 of which have for their object the supply of the wants of the 

 body, or its preservation from injury. Of these the only one 

 which it is desirable here to notice is that of sucking, as per- 

 formed by the young Mammiferous animal. In this opera- 

 tion there is a very complex union of the actions of different 

 muscles, those of respiration, together with those of the 

 tongue and lips. So beautifully adapted is this combination 

 to its designed purpose, that it could not be better contrived 

 by the longest experience or the most careful study. Yet we 

 find that the young Mammal commences to perform it without 

 any experience or study, the instant that its lips touch the 

 nipple of its parent. And that it is a reflex action, dependent 

 upon the spinal cord alone for its performance, and requiring 

 a stimulus to excite it, is proved by these remarkable facts ; 

 that it has been performed by human infants which have 

 been born destitute of brain, and which have lived for some 

 hours ; and also by puppies whose brain had been removed. 

 These last not only sucked a moistened finger, when it was 

 introduced between their lips, but also pushed out their feet, 

 as the young animal naturally does against the dugs of the 

 parent. 



473. There are many irregular actions of the Spinal Cord, 

 however, the careful study of which is of the highest impor- 

 tance to the Medical Man. It is probable that all convulsive 

 movements are produced through its agency ; these being for 

 the most part of a reflex character, that is, dependent upon 

 some stimulus or irritation which acts through the nervous 

 circle described in 470. Thus, convulsions are not unfre- 

 quent in children during the period of teething ; and are then 



