CHAPTER XII. 



Reflex action. A decerebrate frog is sus- 

 pended by the lower jaw. The following experi- 

 ments are to be made upon it : 



1. Gently pinch the toe of one foot with forceps ; 

 the leg is drawn up. When again quiescent pinch 

 the toe more firmly ; not only the one, but both 

 legs are drawn up, and there may also be a move- 

 ment of the upper limbs (spread of excitation). 



2. Stimulate the toe (a) with single and (<5) with 

 interrupted induced currents. Determine at what 

 distance of the secondary coil from the primary 

 the reflex response is elicited in each case (effect 

 of summation). 



3. Touch one flank with a glass rod moistened 

 with acetic acid ; the foot of the same side is raised 

 to rub off the irritant ; if that foot is held down the 

 other foot may be used {purposeful actio^i) . 



4. Having washed off the acetic acid and allowed 

 the frog to become quiescent allow the extremity 

 of the toes to dip into dilute sulphuric acid (i per 

 1,000). Count the time in half-seconds which 

 elapses between the application of the acid and the 

 withdrawal of the toe. Wash the acid off immedi- 

 ately after the withdrawal. Repeat this observation 

 at intervals of a few minutes, and take the average 

 time of response (Turc&s method). 



