38 DR. HILL, FROM REFLEX ACTION TO VOLITION. 



elaborate investigations which they have made into the 

 working of the nervous system in this animal. We have 

 probably all of us made such observations as are necessary to 

 determine its fundamental properties. Watch the jelly-fish 

 as it feeds on a rocky coast. The rhythmic pulsations of its 

 pellucid bell bear it gently to and fro within a closely circum- 

 scribed area. At one moment the wave washes it close to 

 the rock ; at the next it has turned on to its side and a few 

 pulsations carry it safely out of danger. However difficult it 

 may be to compare its sensations with our own, they are 

 undoubtedly of such a nature as to give it warning of danger, 

 or rather to produce the movements by which the danger is 

 escaped. What a contrast there is between the beautiful 

 sentient and motile organism at work in the sea and the 

 helpless lump of jelly cast up on the sand. As long, however, 

 as it has life the function by which its movements are 

 determined can be shown to exist. Stroke the stranded 

 jelly-fish with your finger, and if it still lives each stroke is 

 answered by an attempted contraction of the bell, a move- 

 ment which follows the stimulus with unvarying regularity, 

 after an easily-determined interval of time. The only 

 evidence which we can obtain of the functions of the nervous 

 system in the jelly-fish, relates to this unerring mechanical 

 response to stimulus ; Reflex Action. 



To reflex action there are progressively added other 

 functions, of the nature of which we can only form an 

 imperfect picture by a process of subjective analysis, but the 

 existence of which we infer from their effects in the exhibition 

 of what we may term without staying to define or limit the 

 expression " the power of choice." 



Compare the frog with the jelly fish. The healthy, 

 uninjured frog displays in its behaviour evidences of a power 

 of selecting its actions. Frighten it and it may jump away, 

 or it may under apparently exactly similar conditions refuse 

 to move. Remove the brain of the frog (an operation which 

 it bears with remarkable impunity), and carefully keep it 

 moist and fed, and for the rest of its life, which may easily be 

 prolonged for a year or eighteen months, we have in our 

 hands a machine which responds infallibly to every stimulus, 

 but never makes a move in the absence of an easily 

 recognised provoking cause. 



It is easy to show, however, that there are many actions 

 over which the uninjured frog has no control — which are 

 purely reflex — and my object is to trace the relation to one 



