Functions of the Spinal Cord. 607 



been mentioned elsewhere that during the breeding season the thumb 

 of the male frog is greatly enlarged by the formation of large papillae 

 upon it. The spinal cord is, at this season, also subject to much stronger 

 excitability than at other times. The instinct of the frog at this season, 

 is to grasp an object, naturally the female, and to hold on indefinitely, 

 sometimes for weeks. But he will also grasp other objects, and while 

 he is thus holding on, if he be decapitated, or the brain cut away, the 

 grasp is not relaxed, which shows that the contraction of the muscles 

 of these fore limbs is due to reflex action from the stimulus of the 

 touch of the body in contact with the thumb. If the posterior part of 

 the bod} 7 be cut away, the grasp of the thumb will continue, but it will 

 relax immediately when the part of the cord which receives the nerve 

 trunks from the fore limbs is cut out or disconnected. 



Again, if, after the brain is gone or disconnected from the spinal cord, 

 the skin on the side of the frog be touched with acetic acid, the foot on 

 the same side will be raised and rubbed against the place as if to rub 

 off the acid ; and still more remarkable, if that foot be held so it cannot 

 be used, the other will, after a time, be extended across the body in an 

 effort to do the rubbing. ( Huxley. ) To a frog in possession of his 

 brain, the application of acetic acid to the part indicated, is painful. 

 But when the stimulus reaches the spinal cord only, and is reflected 

 from there to the limbs, there is every reason to conclude that sensation 

 is not aroused. It may be doubted in this case whether the spinal cord 

 alone was responsible for all these rather complicated muscle combina- 

 tions. In all probability it was assisted by the centers in the medulla 

 oblongata. The account is not sufficiently explicit as to the exact point 

 at which the section of the brain was made. It is not likely that the 

 frog possesses sensibilities different from those of the salamander, an 

 amphibian like himself. His consciousness depends, like that of most 

 other vertebrates, on the more anterior ganglia of the brain. The per- 

 formance of reflex actions does not, however, depend upon the absence 

 of consciousness. If, for example, the foot of a ticklish person be 

 touched with a feather, although the person may be conscious of what 

 is going on, the foot is withdrawn without any effort of his will, and 

 even against it. The action is the same in this case as it would be in 

 the unconsciousness of sleep, for the foot would be withdrawn just the 

 same. In both cases the movement of the foot is reflex. In the first 

 one the irritation is strong enough to arouse the consciousness as well ; 

 in the last one, it is not. Thus it appears that reflex action does not de- 

 pend one way or another on consciousness, but both the action and the 

 consciousness depend on the stimulation. In the case of our frog, his 

 actions in withdrawing his tickled limb, and in attempting to rub off 

 the acetic acid, are just what they would have been if he had possessed 



