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 (§ 47 9). 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 
