222 ANIMAL AUTOMATISM v 



In order to move the legs in this way, a 

 definite co-ordination of muscular contractions is 

 necessary ; the muscles must contract in a certain 

 order and with duly proportioned force; and 

 moreover, as the feet are drawn away from the 

 source of irritation, it may be said that the 

 action has a final cause, or is purposive. 



Thus it follows, that the grey matter of the 

 segment of the man's spinal cord, though it is 

 devoid of consciousness, nevertheless responds to 

 a simple stimulus by giving rise to a complex set 

 of muscular contractions, co-ordinated towards a 

 definite end, and serving an obvious purpose. 



If the spinal cord of a frog is cut across, so as 

 to provide us with a segment separated from the 

 brain, we shall have a subject parallel to the 

 injured man, on which experiments can be made 

 without remorse ; as we have a right to conclude 

 that a frog's spinal cord is not likely to be con- 

 scious, when a man's is not. 



Now the frog behaves just as the man did. 

 The legs are utterly paralysed, so far as voluntary 

 movement is concerned ; but they are vigorously 

 drawn up to the body when any irritant is applied 

 to the foot. But let us study our frog a little 

 farther. Touch the skin of the side of the body 

 with a little acetic acid, which gives rise to Jill 

 the signs of great pain in an uninjured frog. In 

 this case, there can be no pain, because the appli- 

 cation is made to a part of the skin supplied with 



