EFFECT OF TEMPERATURE ON PULSATION 329 



30° C. to 38-5° C. How regularly the frequency of pulsation 

 is increased, and the amplitude diminished, with the rise 

 of temperature is shown in fig. 173. 



In the record just given there is observable an arrest of 

 pulsation when the specimen was subjected to as high a 

 temperature as 38° C. But by accustoming it to warmth, 

 the plant can resist even higher temperatures. Thus I kept 



Fig. 173. — Effect of continuous rise of temperature from 

 30° C. to 38 -5° C. 



several specimens in a glass-house, the temperature in 

 which at midday was 37° C. These specimens could be 

 exposed to a temperature as high as 45° C. without the 

 arrest of the pulsation. I reproduce here a record (fig. 174) 

 where the specimen was gradually raised from 36° C. to 

 42° C, and then allowed to cool and return to the tempera- 

 ture of 30° C. It will be seen that the amplitude of pulsa- 

 tion was continuously decreased, yet there was no arrest 

 even at 42° C. On cooHng, the amplitude was restored to 

 the original value. 



I have shown that under excessive cooling the force 

 of expansion is reduced, in consequence of which there is an 

 arrest towards systole. With excess of heat, on the other 



