CHAPTER XXVI 



EFFECTS OF TEMPERATURE ON AUTONOMOUS RESPONSES 



Increase of frequency and diminution of amplitude of pulsation with rising 

 temperature — Converse effect of fall of temperature — Similar effect in cardiac 

 pulsation — Effect of the reduction of temperature to the thermo-tonic minimum 

 — Explanation of diminution of amplitude of pulsation with rise of temperature 

 — Anomalous use of the word ' relaxation ' — Simple versus additive character 

 of individual pulsation. 



It is my intention in the course of the next chapter to 

 make a comprehensive review of the similarities in all their 

 characteristics of rhythmically responding tissues, both vege- 

 table and animal. In the present chapter, then, we shall 

 confine our attention to a study in detail of the influence 

 of temperature in modifying the amplitude and period of 

 rhythmic autonomous responses, exemplified in the case of 

 plant-tissues by Desmodium and in that of the animal by- 

 cardiac muscle. 



As then we are about to study the effect of temperature 

 on the period and amplitude of vibration of the Desmodium 

 leaflet, it is clear that our first difficulty must be the securing 

 of a specimen in which both are, to begin with, more or 

 less uniform ; for the pulsation of Desmodium, like that of 

 the isolated frog's heart used for experiments, is often 

 irregular. It is thus only by careful selection that one can 

 obtain suitable experimental subjects. A moderate increase 

 of the internal hydrostatic pressure, however, will often have 

 the effect of rendering the responses sufficiently uniform. 



Regulation of temperature. — The second difficulty in 

 this investigation lies in subjecting the plant to the required 

 rise or fall of temperature. A rise of temperature may be 

 secured by any one of three different methods, (i) A spirit 



