602 THE HUMAN BODY. 



these soon cease, the legs hang down, and the creature comes 

 to rest. If one flank be now gently scratched with the point 

 of a pencil a reflex movement occurs, limited to the muscles 

 of that region; they twitch, somewhat as a horse's neck when 

 tickled by flies. If a pinch with small forceps be given 

 at the same spot, more muscles on the same side come 

 into play; a harder pinch causes also the hind leg of that 

 side to be raised to push away the offending object; more 

 violent and prolonged irritation causes all the muscles of 

 the body to contract, and the animal is convulsed. Here 

 then we see that a feeble stimulation causes a limited and 

 purpose-like response; stronger causes a wider radiation of 

 efferent impulses from the cord and the contraction of 

 more muscles, but still the movements are co-ordinated to 

 an end; while abnormally powerful stimulation of the sen- 

 sory nerves throws all the motor fibres arising from the 

 cord into activity, and calls forth inco-ordinate spasmodic 

 action. The orderly movements are very uniform for a given 

 stimulation; if the anal region be pinched, both hind legs are 

 raised to push away the forceps ; if a tiny bit of bibulous paper 

 moistened with dilute vinegar be put on the thigh, the lower 

 part of that leg is raised to wipe it off; if on the middle of the 

 back near the head, both feet are wiped over the spot; if on 

 one flank, the leg and foot of that side are used, and so on ; 

 in fact, by careful working, the frog's skin can be mapped 

 into many regions, the application of acidulated water to each 

 causing one particular movement, due to the co-ordinated 

 contractions of muscles in different combinations, and never, 

 under ordinary circumstances, any but that one movement. 

 The above purpose-like reflex movements may all be charac- 

 terized as defensive, but all orderly reflexes are not so. For 

 example, in the breeding season the male frog clasps the female 

 for several days with his fore limbs. If a male at this season 

 be decapitated and left to recover from the shock, it will be 

 found that gently rubbing his sternal region with the finger 

 causes him to clasp it vigorously. 



Disorderly Reflexes or Reflex Convulsions. These come 

 on when an afferent nerve-trunk is stimulated instead of the 

 tactile end organs in the skin ; or when the skin is very power- 

 fully excited; or, with feeble stimuli, in certain diseased states 

 (pathological tetanus), and under the influence of certain 

 poisons, especially strychnine. If a frog or a warm-blooded 



