NEKVES OF SENSE AND OF MOTION IN THE HORSE. 27 



muscular system. Thus impressions made on the extremities 

 of nerves end in muscular acts set up through the nerves by 

 certain conditions of the brain. Moreover, physiologists have 

 discovered that there are two kinds of nerves namely, nerves 

 of sense and nerves of motion ; or, as these are sometimes 

 named, afferent nerves and efferent nerves the nerves of sense 

 being termed afferent, because they carry impressions to the 

 central nervous organs ; and the nerves of motion efferent, 

 because they convey from the brain or centre the stimulus by 

 which muscular fibres are called into activity. In all familiar 

 instances in which motion follows impressions, there is inter- 

 posed a state of consciousness, or rather two states of con- 

 sciousness the one constituting a sensation, the other a voli- 

 tion, or that act which precedes muscular action. But there 

 is also a kind of cases in which muscular movement arises 

 without volition, and to this, of late, the name of reflex action 

 has been applied. To illustrate the difference : if a man sit- 

 ting with his foot on the fender sees the tea-kettle about to 

 boil over, he deliberately withdraws his foot. Here the sensa- 

 tion in the act of sight is followed by a voluntary act; the 

 impression on the eye is followed by one state of consciousness 

 and then a volition that is, another state of consciousness 

 arises able to determine the contraction of the muscles neces- 

 sary for the withdrawal of the foot. If, however, the tea- 

 kettle boils over without any previous warning, and some 

 drops of hot water fall suddenly on his foot, the foot is with- 

 drawn instantly, without any intervening volition. This is a 

 case of reflex action. Here, however, there is one state of 

 consciousness namely, the sensation consequent on the im- 

 pression made by the hot water on the nerves of the foot ; the 

 state of consciousness which is wanting is the consciousness 

 of volition. But there are cases of reflex action known, both 

 in man and in the animals beneath him, in which there is 



