Organic Nature s Riddle 317 



msation, and gives rise to an influence proceeding outwards 

 the muscles, resulting in definite and appropriate motions. 

 There are cases in which responsive actions take place 

 ider very abnormal conditions — as after a rupture of part 

 a man's spinal cord, or the removal of the whole brain in 

 >wer animals, such as the frog. A man so injured may have 

 tterly lost the power of feehng any stimulation — pricking, 

 itting, or burning — of his legs and feet, the injury prevent- 

 ig the conveyance upwards to the brain of the influence 

 jcessary to produce sensation, and arresting it in the 

 >inal cord below the point of injury. Nevertheless, such a 

 ^lan may execute movements in response to stimuli just as 

 if he did feel, and often in an exaggerated manner. He will 

 withdraw his foot if tickled with a feather, just as if he 

 felt the tickling, which he is utterly incapable of feeling. 

 Similarly a decapitated frog will make with his hind legs 

 the most appropriate movements to remove any irritating 

 object apphed to the hinder part of .its body. Such action 

 is termed ' reflex action,' on the supposition that the influence 

 conveyed inwards by nerves going from the skin to the 

 spinal cord is reflected back from that cord to the muscles 

 by the other set of nerves without any intervention of 

 sensation. This action of the frog may be carried to a very 

 singular extreme. At the breeding season the male frog* 

 tightly grasps the female behuad her arms, and to enable 

 him the more securely to maintain his hold, a warty pro- 

 minence is then developed on the inner side of each of his 

 hands. Now if such a male frog be taken, and not only 

 decapitated, but the whole hinder part of the body removed 

 also, so that nothing remains but the fragment of the trunk 

 from which the two arms with their nerves proceed, and if 

 under these circumstances the Avarty prominences be touched, 

 the two arms will immediately close together like a spring, 

 thus afibrding a most perfect example of reflex action. It 



