ACTION OF THE SPINAL CORD AS A NERVE-CENTRE. 685 



one to three minutes until the effects of the shock and local irritation have subsided, if 

 we then, when the animal has become perfectly quiet, cover it with a bell-glass, and 

 finally, if we remove all possibility of jarring the table on which the animal is placed, 

 there is no movement of muscles. In making an experiment of this kind, we occasionally 

 see movements which are due to a very feeble impression, such as a breath of air or a 

 jar from the street, but which is perfectly evident to the observer ; and, when a move- 

 ment is once made, this gives rise to another impression, and thus, successive actions of 

 the muscles may take place. The movements in jumping are so simple that they seem, 

 sometimes under these conditions, to be voluntary. The effect of feeble excitations is 

 also very marked in animals poisoned with strychnine ; but, even here, we do not have 

 movements unless an impression be first made upon the sensory nerves. When we 

 come to experiments upon the mammalia, there can hardly be any question of this kind ; 

 for here, as the rule, no movements are observed after the encephalic ganglia have been 

 removed, unless the sensory nerves be pretty strongly stimulated. Analogous phenomena 

 are observed in the lower extremities, in cases of paraplegia in the human subject. 



The next important question to determine is with regard to the nature of movements 

 excited by external stimulation in decapitated animals, especially frogs ; for some of these 

 movements are so regular as to appear to be connected with sensation and volition. The 

 experiments of Pfluger upon this point are very remarkable. These have been repeatedly 

 confirmed, and there can be no doubt with regard to their accuracy. Pfluger carefully re- 

 moved from a frog the entire encephalon, leaving only the spinal cord. He then touched 

 the surface of the thigh over the inner condyle with acetic acid, to the irritation of which 

 frogs are peculiarly sensitive. The animal thereupon rubbed the irritated surface with the 

 foot of the same side, apparently appreciating the locality of the irritation, and endeavor- 

 ing, by a voluntary effort, to remove it. The foot of this side was then amputated, and 

 the irritation was renewed in the same place. The animal made an ineffectual effort to 

 reach the spot with the amputated member, and, failing in this, after some general move- 

 ments of the limbs, rubbed the spot with the foot of the opposite side. Although this 

 experiment does not always progress precisely in the manner described, it has succeeded 

 perfectly in so many instances as to lead some physiologists to conclude that sensation 

 and volition are not entirely abolished by removal of the encephalon, at least in frogs. 



The remarkable phenomena just detailed are to be regarded from two points of view : 

 first, with reference to their bearing upon the question of the existence of perception and 

 volition in the spinal cord of the frog ; and second, the question of the application of 

 these phenomena to the physiology of the cord in man and the higher classes of animals. 

 The conditions of the experiment in the frog are simply these : Instead of exposing the 

 surface to a single and instantaneous stimulation, the excito-motor effects of which are 

 observed as a direct response to the irritation and immediately cease, we have, by the 

 application of acetic acid to the surface, a prolonged impression upon the sensory nerves, 

 which, by virtue of the anatomical connections between the different parts of the cord, 

 is probably dispersed throughout the entire spinal axis. That powerful impressions may 

 be thus dispersed, there can be no doubt, as we shall see farther on. The phenomena 

 under consideration certainly point to an appreciation by the cord of the locality of a 

 powerful impression, and this could be manifested in an animal only by an apparent 

 muscular effort to reach the irritated spot ; but we can hardly reason from this fact that, 

 in man and the higher animals, the spinal cord shares with the brain the power of appre- 

 ciating what we know as sensation and of generating the stimulus of true voluntary 

 movement. If a sudden and very powerful painful impression be made upon the surface 

 in man under normal conditions, the hand may be instantly applied to the affected part, 

 apparently before we really appreciate the pain or have time to make a distinct effort of 

 the will ; but the connections between the different parts of the cerebro-spinal axis do 

 not permit us to isolate the action of the cord. Certain it is that, in the higher animals, 

 after removal of the encephalon, and in experiments upon decapitated criminals and 



