118 ELEMENTARY PHYSIOLOGY. [XI. 



7. 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. 



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

 leg ; that leg will immediately be drawn up. 



9. Take two glasses, fill one with dilute sulphuric 

 acid ('1 p.c.) and the other with water: lower 

 the frog until the tip of one of the toes just 

 touches the dilute sulphuric acid. In a short 

 time the foot will be withdrawn. At once let 

 the foot dip into the second glass containing 

 water, in order to wash away the acid. Measure 

 with a rapidly beating metronome, the time 

 between the moment when the toe comes into 

 contact with the acid and the moment when it 

 is withdrawn. Make, at intervals of a few 

 minutes, three such observations, and take the 

 mean of the three. 



10. Cut a small piece of blotting-paper one or two 

 mms. square, moisten it with strong acetic acid, 

 and place it on the flank of the animal. The 

 leg of the same side will be speedily drawn up 

 and swept over the flank as if to remove the 

 piece of paper. 



11. Place similar pieces of paper dipped in acetic 

 acid on different parts of the body; different 

 movements will be witnessed in consequence; 



