v SPINAL COED AND NERVES 339 



by long practice became as it were materialised and automatic, 

 and were transmitted by inheritance. Evidence for the organisa- 

 tion of what were at the outset voluntary acts, lies both in the 

 fully unconscious co-ordinated reflexes, which we are able to carry 

 out not merely in sleep but also in the waking state, and in the 

 fact that many complex actions that were voluntary at first (e.g. 

 walking, reading, piano-playing, etc.) become, after long practice, 

 mechanical, and are carried out with perfect regularity without 

 the intervention of the will or the least effort of attention. 



In order to judge objectively of the psychical or mechanical 

 character of a given spinal reaction, it is necessary, according to 

 Pflliger and Auerbach, to see if it varies from one moment to 

 another with the variations in external relations. If the individual, 

 when prevented from carrying out a given movement adapted to 

 the removal of an obnoxious stimulus, employs another action 

 directed to the same end, this proves it to be possessed of sentient 

 functions, because from one moment to the next, without any pre- 

 existent mechanism organised by long practice, it knows how to 

 modify or change the character of the reaction, so as to adapt 

 it to the required end. Evidence of such a capacity is brought 

 forward by these authors. They observed that a decerebrated 

 frog, when a drop of acid falls on its right flank, or, better, when 

 a bit of paper soaked in acid is applied to it, always uses its right 

 leg to wipe away the irritant. If the right leg is amputated, it 

 first, makes ineffective efforts with the stump, and then employs 

 its left leg. If, after amputating the right leg, the acid is applied 

 to the right side of the back, the frog again makes ineffectual 

 attempts with the stump, and then stops. But on applying the 

 acid to the left side of the back also, the frog uses its left foot to 

 wipe itself on the left as well as on the right side. 



Pfliiger insisted on these phenomena as evidence that the 

 spinal cord of the frog is capable of at least rudimentary psychical 

 functions. According to other authors, on the contrary, these 

 actions, besides being rare and generally incomplete, are capable 

 of a purely mechanical explanation. The fact that when the 

 limb which the animal uses for removal of the cutaneous stimulus 

 has been amputated, the limb of the opposite side is resorted to 

 for' the same purpose after ineffective attempts with the stump, is 

 held to mean that the local excitation, owing to the longer contact 

 of the stimulus on the skin, has become more intense, and has 

 spread from one half of the cord to the other. But if Pfliiger's 

 description is studied in all its significant details, this mechanical 

 explanation is obviously inadequate. 



Foster, on the other hand, points out that spontaneous move- 

 ments (automatic movements proper), such as occur in the entire 

 absence of external stimuli, are never seen in the spinal frog. 

 This fact appears to him irreconcilable with the existence of any 



