REFLEX ACTION. 37 



nor if its feet were held in fire. So with the frog. After its 

 head is cut off, or, what amounts to the same tiling, its brain 

 destroyed, it cannot feel anything, and, of course, cannot have 

 any pain. So, if in any of the experiments with the frog after 

 its head is cut off it seems to be suffering or attempting to 

 get away, remember, it cannot feel. 



Kill the frog as directed on page 13. As soon as it is 

 motionless, take it out of the jar. By bending its head, find 

 the joint between the head and the backbone. Lay the frog 

 on a board, and thrust the scalpel through the body at the 

 joint just found, thus completely severing the spinal column 

 and spinal cord. Run a wire through the opening thus made 

 into the skull, and stir about to destroy the brain. 



After a while suspend the frog from a ring of a retort 

 stand by a hook through the jaw. 



1. With a pair of forceps pinch one of the frog's toes. 

 Now, if the frog were alive it would feel the pinch, and a 

 strong pinch would cause pain. Now that the brain is de- 

 stroyed, it feels nothing. Still it draws up the foot. Repeat 

 the experiment with the other foot. 



2. Lay the frog on its abdomen, and dissect away the skin 

 from the back of one of the thighs. Separate the muscles 

 along the noticeable groove in the posterior dorsal part of the 

 thigh, using for this work the handle of the scalpel. There 

 should be found the white, thread-like Sciatic Nerve. Care- 

 fully loosen this from the surrounding tissues, and pass one 

 blade of a pair of sharp scissors under it. Steady the hand, 

 so as not to give any motion to the suspended frog from the 

 act of cutting, and, while closely watching the foot, cut the 

 nerve. The muscles of the leg shorten, and jerk the foot. 



3. Again pinch the toes of the limb whose sciatic nerve is 

 cut. It does not move. Pinch the toes of the other foot ; the 

 leg draws up as before. 



