CHAPTER XXV 



EFFECT OF TEMPERATURE ON RHYTHMIC PULSATION OF 

 DESMODIUM GYRANS 



Effect of lowering of temperature on rhythmic pulsation of cardiac tissue — • 

 Similar effect on the pulsation of Desmodium — Increase of systolic 

 limit during cooling — Minimum temperature for arrest of pulsation — 

 Arrest by cooling and subsequent revival by warming — Increase of 

 diastolic limit during warming — Effect of rise of temperature on the pul- 

 sation of frog's heart — Similar effect on the pulsation of Desmodium — 

 Effect of rise above and return to normal temperature — Diminution of 

 systolic contraction during rise of temperature — Increase of systolic 

 contraction during fall of temperature — Permanent arrest due to 

 heat-rigor. 



In the course of our study of automatic pulsation of Des- 

 modium we shall find striking similarities between the 

 rhythmic activities of the plant and animal tissues. In the 

 present chapter we will study in detail the effect of tem- 

 perature in modifying the amplitude and period of the 

 spontaneous movements. 



I have already described the thermal chamber by means 

 of which the temperature of the plant can be regulated. 

 Temperature, as we have seen, may be raised to any degree 

 by the adjusting of the heating current which passes through 

 a coil of German silver. Lowering of temperature, on the 

 other hand, is effected by allowing a stream of cooled air to 

 pass through the chamber containing the specimen. 



Effect of Lowering of Temperature 



In the rhjrthmic pulsation of frog's heart the marked 

 effect of variation of temperature is to change the period and 

 modify the amplitude of pulsation. Lowering of tempera- 

 ture has the ef ect of lengthening the period and enhancing 



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