IV 



REFLEX ACTION 49 



7. The controlled reflex may look externally very much 

 like a true conation. In particular cases indeed it may be 

 impossible to determine with certainty the class to which 

 an act belongs. If an irritant is not removed from the 

 windpipe by a cough, one goes on coughing. The action 

 is continued till satisfaction is obtained. In this case our 

 will seems at times to co-operate. Yet the mechanical 

 element may suffice of itself and the coughing fit may in 

 fact be uncontrollable. In this case the explanation is 

 simply that the stimulus is capable of calling forth 

 repetitions of the response as long as it persists or until 

 exhaustion sets in. In other cases additional stimulus 

 may increase the excitement so that it spreads to other 

 parts of the body, which by acting suitably give relief. 

 Thus : 



..." if a flank of a brainless frog be very lightly touched, the 

 only reflex movement which is visible is a slight twitching of the 

 muscles lying immediately underneath the spot of skin stimulated. 

 If the stimulus be increased, the movements will spread to the 

 hind-leg of the same side, which frequently will execute a move- 

 ment calculated to push or wipe away the stimulus. By forcibly 

 pinching the same spot of skin, or otherwise increasing the 

 stimulus, the resulting movements may be led to embrace the 

 fore-leg of the same side, then the opposite side, and finally, almost 

 all the muscles of the body." l 



It would seem from this account as a whole that the suc- 

 cessive modifications of the response, which at one stage 

 have a purposive appearance, are due rather to something 

 of a mechanical nature such as the overflow of nervous 

 excitement. Even an excised muscle varies its response 

 to stimulus in a manner suited to the ordinary behaviour 

 of muscle when doing its work within the organism. 

 For if under a certain stimulus it lifts a given load a 

 certain height, it might be inferred on mechanical principles 

 that it would only lift double the weight half the height. 

 But this is not necessarily true. 



..." The height to which the weight is raised may be in the 

 second instance as great, or even greater, than in the first. That 

 is to say, the resistance offered to the contraction actually augments 



Foster, I. p. 183. 



