262 EXPERIMENTAL PHYSIOLOGY. 



signal is set free. The interval between the two events, 

 calculated from the vibrations of the tuning-fork, gives the 

 reaction time. The experiment must be repeated several 

 times, and the mean of several observations taken. 



4. Inhibition. 



(a.) Take an uninjured frog, place it on its back, and 

 observe that it will not lie in this position, but immediately 

 rights itself. Tie pretty firmly a thick string round each upper 

 arm. This in no way interferes with the movements of the 

 frog, but on placing the animal on its back, it no longer 

 rights itself, but continues to lie in this position for a long 

 time. It may be moved or pulled by the legs, yet it does 

 not regain its normal attitude. Notice the modification of 

 the respiratory movements. 



5. Kircher's Experimentum Mirabile. 



(a.) Take a hen and hold it gently to restrain its move- 

 ments. Bring its bill in contact with a table, and then 

 with a piece of white chalk draw a line directly outwards 

 from its bill. Hold the animal steadily for a few seconds, 

 and on removing the hands gently, it will be found that 

 the hen lies quiescent and does not move for a considerable 

 time. It may be rolled to one side or the other, yet it lies 

 quiescent. 



(b.) Repeat the same process, but instead of a white line 

 lay a straw or white thread over the base of its bill. In a 

 short time the animal becomes quiescent. Notice the 

 alteration of the heart-beat and the depth and number of 

 the respirations. 



