CHAP. XI.] FUNCTIONS OF THE CORD. 309 



as well as cold-blooded. In the latter, however, they are much 

 more marked ; the nervous force endures much longer in these ani- 

 mals than in the higher classes of mammalia and birds, just as we 

 have already seen that the muscular power does, although we have 

 no reason to suppose that either force is more energetic, because it 

 is more enduring. On this account, cold-blooded animals must be 

 selected for exhibiting the phenomena; and accordingly hosts of 

 frogs, salamanders, snakes, turtles, and fishes have fallen a prey to 

 the experimental researches of the numerous physiologists who have 

 devoted themselves to these investigations. 



The following experiments serve to illustrate these actions : 



If a frog be pithed by dividing the spinal cord between the occi- 

 pital hole and the first vertebra, an universal convulsion takes place 

 while the knife is passing through the nervous centre. This, how- 

 ever, quickly subsides ; and, if the animal be placed on a table, he 

 will assume his ordinary position of rest. In some exceptional 

 cases, however, frequent combined movements of the lower extre- 

 mities will take place for a longer or shorter time after the opera- 

 tion. When all such disturbance has ceased, the animal remains 

 perfectly quiet, and as if in repose, nor does there appear to be the 

 slightest expression of pain or suffering. He is quite unable to 

 move by any voluntary effort. However one may try to frighten 

 him, he remains in the same place and posture. If now a toe be 

 pinched, instantly the limb is drawn up, or he seems to push away 

 the irritating agent, and then draws up the leg again into its old 

 position. Sometimes a stimulus of this kind causes both limbs to 

 be violently moved backwards. A similar movement follows sti- 

 mulation of the anus. If the skin be pinched at any part, some 

 neighbouring muscle or muscles will be thrown into action. Irrita- 

 tion of the anterior extremities will occasion movements in them ; 

 but it is worthy of note, that these movements are seldom so ener- 

 getic as those of the lower extremities. 



It is not out of place to state here, that phenomena of this kind 

 are not confined to the trunk and extremities which are supplied by 

 spinal nerves only. The head and face with which the encephalon 

 remains in connexion exhibit similar actions. The slightest touch 

 to the margin of either eyelid, or to the surface of the conjunctiva, 

 causes instantaneous winking; the attempt to depress the lower 

 jaw, for the purpose of opening the mouth, is resisted; and the act 

 of deglutition is provoked by applying a mechanical stimulus to the 

 back of the throat. 



The stimuli which excite these movements are those ordinary 



