410 REFLEX ACTIONS. 



up exactly the same temperature renders it unsuitable for com- 

 parative experiments. 



In all the above experiments the movements produced bear 

 marks of purpose. As the result of stimulation of a particular 

 region of the surface of the body, we find a complicated move- 

 ment, a movement brought about by the contraction of certain 

 muscles and sets of muscles, acting in a definite combination 

 and sequence. The movement thus produced is apparently 

 directed towards an end. Thus when the foot is pinched or 

 irritated by the acid, the resulting movements appear at least 

 directed towards, and frequently actually effect, the withdrawal 

 of the foot from the offending object ; when the flank is pinched, 

 the movement is such as tends to thrust away the points of the 

 forceps ; when the anus is pinched to kick away the forceps, 

 and so on. 



This purposeful character of reflex actions may be still more 

 conveniently shown by adopting the following method : 



06s. VIII. Arrange the frog with the legs alone free ac- 

 cording to the second method given above. Cut small pieces 

 of blotting-paper about 1 or 2 millimetres square, dip them in 

 strong acetic acid, remove from them all superfluous acid, and 

 then place them on definite regions of the skin. In this way the 

 stimulus may be limited to very small areas chosen at pleasure ; 

 and it will be found that very different movements of the hind 

 limbs will be produced by applying the morsel of paper to dif- 

 ferent regions of the body. Thus if the morsel be placed on 

 the heel of one foot, both feet will be violent^' rubbed together, 

 while the legs remain forcibly extended. If the morsel be 

 placed on one flank, it will be rubbed off by the foot of the 

 same side ; if it be placed in the mid-line of the back, either or 

 both feet will be employed to remove it, and so on. 



The student will do well to map out the limbs and body of 

 the frog into small areas, and to determine the characters of 

 the movements, which result from the stimulation of each 

 area, lie will in this way find abundant instances of an appa- 

 rent purpose. 



o/,s. IX. It has been seen that where the morsel of aeid 

 paper is placed, say on the right flank, it is the right leg, and 

 the right leg only, which under ordinary circumstances is used 

 to rub off the paper. Choosing a strong frog, in which reflex 

 action has been found to be highly developed, suspend it ac- 

 conling to the second method, hold the right leg firmly down, 

 or load it with a greater weight than the leg is able to lift, and 

 apply a morsel of acid paper to the right flank. Twitchin'gs 

 and convulsive movements of the right leg are first witnessed, 

 < v and then the /<;/'/ leg is brought up to rub the right flank. 



I'laee a similarly strong frog svilh powerful reflex capabilities 

 its back on the table. 



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