IX.] ANIMAL AUTOMATISM. 219 



the contrary, it is the seat of extremely remarkable 

 powers. In our imaginary case of injury, the man 

 would, as we have seen, be devoid of sensation in his 

 legs, and would have not the least power of moving 

 them. But, if the soles of his feet were tickled, the 

 legs would be drawn up, just as vigorously as they 

 would have been before the injury. We know 

 exactly what happens when the soles of the feet are 

 tickled ; a molecular change takes place in the sen- 

 sory nerves of the skin, and is propagated along them 

 and through the posterior roots of the spinal nerves, 

 which are constituted by them, to the grey matter 

 of the spinal cord. Through that grey matter, the 

 molecular motion is reflected into the anterior roots of 

 the same nerves, constituted by the filaments which 

 supply the muscles of the legs, and, travelling along 

 these motor filaments, reaches the muscles, which at 

 once contract, and cause the limbs to be drawn up. 



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 seg- 

 ment 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. 



