68 EXPERIMENTAL PHYSIOLOGY. 



strate the latent period, the duration of the after-effect, changes 

 in rate, and escapement. (Fig. 17). 



INFLUENCE OF TEMPERATURE. Continuing with the same pre- 

 paration obtain records with the heart at the following tempera- 

 tures: 4, 10, 20, and 30 C. These temperatures can be 

 obtained by pouring Ringer's solution of the corresponding 



FIG. 20. Refractory period and compensatory pause in the heart. Stimulation at X. 



temperature over the heart. How does temperature influence 

 the rate and amplitude of the beat? What modification takes 

 place in the A-V interval? 



EXTRA SYSTOLE. Remove the heart by cutting widely around 

 the base. Drop it in Ringer's solution. After studying it 

 there for a short time, pin the base to a frog board and attach 



