REFLEX ACTION 57 



If this experiment be made soon after the operation of 

 removing the brain, or if much blood has been lost, the 

 leg may be drawn up slowly instead of sharply. 



4. Gently tickle one flank with a feather or a blunt 

 needle; a contraction of the flank muscles of that side 

 will be observed. 



5. Pinch the same spot rather sharply with a pair of 

 forceps; the leg of the same side will be first extended, 

 and then drawn up and swept over the flank, the move- 

 ment tending to thrust away the points of the forceps. 



6. Pinch with the forceps the skin round the anus; 

 both legs will be drawn up and thrust out again; the 

 movement tending as before to sweep away the points 

 of the forceps. 



Leave the animal alone for five minutes and watch it 

 carefully : if no disturbing circumstances are brought to 

 bear on it, it will remain perfectly motionless. 



7. Place the animal on its back ; it will make no effort 

 to regain its normal position, i.e. all sense of equilibrium 

 has been lost. 



8. Pass a hook through the lower jaw, and fasten it 

 to the cross bar of a stand so that the body can be raised 

 up and down. The hind-limbs, after a few movements 

 of flexion and extension, will remain pendant and 

 motionless. 



9. Gently pinch the tip of one of the toes of either 

 leg; that leg will immediately be drawn up. 



10. Fill a beaker with water; and place a little acetic 

 acid -5 to 1 p.c. acid in a watch-glass: let the tip of one 

 of the toes of the frog touch the acid. In a short time 



