REFLEX FUNCTION OF THE SPINAL CORD. 497 



If the foot be pinched, or burned with a lighted taper, it is withdrawn ; 

 and (if the animal experimented on be a Frog) the animal will leap 

 away, as if to escape from the source of irritation. If the cloaca be 

 irritated with a probe, the hind-legs will endeavour to push it away. 



876. Now the performance of these, as well as of other movements, 

 many of them most remarkably adapted to an evident purpose, might 

 be supposed to indicate, that sensations are called up by the impres- 

 sions ; and that the animal can not only feel> but can voluntarily direct 

 its movements, so as to get rid of the irritation which annoys it. But 

 such an inference would be inconsistent with other facts. In the first 

 place, the motions performed by an animal under such circumstances 

 are never spontaneous, but are always excited by a stimulus of some 

 kind. Thus, a decapitated Frog, after the first violent convulsive 

 movements occasioned by the operation have passed away, remains at 

 rest until it is touched : and then the leg, or its whole body may be 

 thrown into sudden action, which immediately subsides again. In the 

 same manner, the act of swallowing is not performed, except when it 

 is excited by the contact of food or liquid ; and even the respiratory 

 movements, spontaneous as they seem to be, would not continue, unless 

 they were continually re-excited by the presence of venous blood 

 in the vessels. These movements are necessarily linked with the 

 stimulus that excites them ; that is, the same stimulus will always pro- 

 duce the same movement, when the condition of the body is the same. 

 Hence it is evident, that the judgment and will are not concerned in 

 producing them ; and that the adaptiveness of the movements is no 

 proof of the existence of consciousness and discrimination in the being 

 that executes them, the adaptation being made for the being, by the 

 peculiar structure of its nervous apparatus, which causes a certain move- 

 ment to be executed in respondence to a given impression, not by it. 

 An animal thus circumstanced may be not unaptly compared to an auto- 

 maton ; in which particular movements, adapted to produce a given 

 effect, are produced by touching certain springs. Here the adaptation 

 was in the mind of the maker or designer of the automaton ; and so it 

 evidently is, in regard to the reflex or consensual movements of animals, 

 as well as with respect to the various operations of their nutritive sys- 

 tem, over which they have no 'control, yet which concur most admira- 

 bly to a common end. 



877. Again, we find that such movements ^may be performed, not 

 only when the Brain has been removed, the Spinal cord remaining en- 

 tire, but also when the Spinal cord has been itself cut across, so as to 

 be divided into two or more portions, each of them completely isolated 

 from each other, and from other parts of the nervous centres. , Thus, 

 if the head of a Frog be cut off, and its spinal cord be divided in the 

 middle of the back, so that its fore-legs remain connected with the 

 upper part, and its hind-legs with the lower, each pair of members may 

 be excited to movement by a stimulus applied to itself; but the two 

 pairs will not exhibit any consentaneous motions, as they will do when 

 the spinal cord is undivided. Or, if the Spinal cord be cut across, 

 without the removal of the Brain, the lower limbs may be excited to move- 

 ment, by an appropriate stimulus, though they are completely paralysed 



