576 THE HUMAN BODY. 



things applied to them; if, however, the soles of the feet 

 be tickled the legs are thrown into vigorous movement. 

 As a rule^ howevej^orderly reflexes are less jmarked_..and 

 less numerous in the higher animals; in them the organiza- 

 tion is less_nia^hinjerlike^i]ie_spinal cord being more^tjie 

 s^vajitof the larger brain, and less capable of working 

 without directions^ Such animals, when intact, can to a 

 greater extent control the muscular responses which shall 

 be made to stimuli under various conditions; they have less 

 automatic protection in the ordinary risks of life, but a 

 greater range of possible protection. The kujmin__spiBal 

 QprgLcontrolled by the brain, can adapt the rej^ctiojigjiLtlie 

 Body, with great nicety y to a vast variety of conditions ; the 

 frog's cord by itself does this for a smaller number of possi- 

 ble emergencies without troubling at all such brain as the 

 animal has, but is less completely under the control of the 

 higher centres for adaptation to other conditions. The 

 difference being, however, but one of degree and not of 

 kind, it is best to approach the study of the reflex actions 

 of the human spinal cord through an examination of those 

 exhibited by the frog. 



The Orderly Reflex Movements of a Decapitated Frog. 

 For the occurrence of these the following parts must be in- 

 tact; (a) thfi_gnd organs of sensory nerve-fibres ; (b) 

 fibres fr^m theae to the nord- (ri pjferent nbrc^s fro 

 cord to the muscles; (d) the part of the 

 the afferent and efferent fibres; (e) the muscles J3o$cerne( 

 in the movement. If the decapitated animal be suspended 

 vertically after the shock of the operation is over, it makes 

 a few attempts to hold its hind legs in their usual flexed 

 position; these soon cease, the legs hang down, and tfie 

 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, some- 

 what as a horse's neck when tickled by flies. If a pinch bo 

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

 come into play; a harder pinch causes also the hind leg oi 

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

 more violent and prolonged irritation causes all the muscles 



