REFLEX ACTION OF THE SPINAL COED. 305 



point we can only speak positively from our own experiments. 

 If a frog be decapitated, so as to leave only the spinal cord 

 intact, if we wait for from 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 movement is once made, this gives rise to an- 

 other 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 vol- 

 untary. 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 sen- 

 sory nerves be pretty strongly stimulated. Analogous phe- 

 nomena 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 Pfliiger upon 

 this point are very remarkable. These have been repeatedly 

 confirmed, and there can be no doubt with regard to their 

 accuracy. Pfiiiger carefully removed 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. 



