;;S THE PRINCIPLE Ofl Chap. 1. 



at least in part, that some persons find it so difficult to 

 swallow a pill. 



Another familiar instance of a reflex action is the 

 involuntary closing of the eyelids when the surface of 

 the eye is touched. A similar winking movement is 

 caused when a blow is directed towards the face; but 

 this is an habitual and not a strictly reflex action, as 

 the stimulus is conveyed through the mind and not by 

 the excitement of a peripheral nerve. The whole body 

 and head are generally at the same time drawn suddenly 

 backwards. These latter movements, however, can be 

 prevented, if the danger does not appear to the imagi- 

 nation imminent; but our reason telling us that there 

 is no danger does not suffice. 1 may mention a trifling 

 fact, illustrating this point, and which at the time 

 amused me. I put my face close to the thick glass- 

 plate in front of a puff-adder in the Zoological Gardens, 

 with the firm determination of not starting back if the 

 snake struck at me: but, as soon as the blow was struck, 

 my resolution went for nothing, and I jumped a yard or 

 two backwards with astonishing rapidity. My will and 

 reason were powerless against the imagination of a 

 danger which had never been experienced. 



The violence of a start seems to depend partly on the 

 vividness of the imagination, and partly on the con- 

 dition, either habitual or temporary, of the nervous 

 system. He who will attend to the starting of his horse, 

 when tired and fresh, will perceive how perfect is the 

 gradation from a mere glance at some unexpected ob- 

 ject, with a momentary doubt whether it is dangerous, 

 to a jump so rapid and violent, that the animal probably 

 could not voluntarily whirl round in so rapid a man- 

 ner. The nervous svstem of a fresh and hi^hlv-fed 

 horse sends its order to the motory system so quickly, 

 that no time is allowed for him to consider whether 



