EFFECT OF TEMPERATURE ON PULSATION 327 



process of arrest and subsequent revival is clearly seen in 

 fig. 168. It will be noticed that sudden cooling arrested 

 the pulsation at systole and that on gradual warming the 

 rhythmic activity was revived with the gradual restoration 

 of the original amplitude. 



This is still better seen in fig. 169, which gives a mag- 

 nified record of the arrest due to cold, and subsequent 

 restoration of pulsation on return to the temperature of 

 the room. Ice-cold water was applied after the second 

 pulsation. The arrest at systolic contraction is clearly 



Fig. 170. — Effect of rise of temperature on the amplitude and frequency 

 of pulsations of the heart of frog. (Pembrey and Phillips.) 



demonstrated. As the temperature was raised there was 

 increasing expansion, in consequence of which the diastolic 

 excursion was continuously increased. The effect of 

 cooling is thus to increase the force of contraction and 

 diminish that of expansion. The effect of warming is the 

 reverse of these. 



Effect of Rise of Temperature 



We have seen that both in the rhythmic animal and 

 vegetable tissues, the period is increased and amplitude 

 enhanced under the lowering of temperature. The converse 

 is the case with rise of temperature. Fig. 170 shows the 

 effect of rising temperature on the pulsation of the heart 

 of the frog. Similar effects are induced in the pulsation of 

 Desmodium. Fig. 171 gives a series of pulsations of the 

 leaflet at the temperatures of 19 C, 23-5° C, and 28-5° C, 



