CHAPTER XXVI 



EFFECT OF CHEMICAL AGENTS ON THE AUTOMATIC PULSATION 

 OF DESMODIUM GYRANS 



Application of gaseous or liquid reagents — Modifying influence of, tonic 

 condition of specimen, strength, and duration of application — Effect 

 of sugar solution — Effect of alcohol — Action of carbonic-acid gas — 

 Effects of anaesthetics, ether, and chloroform — Action of carbon 

 disulphide — Effect of copper sulphate solution — Effect of potassium 

 cyanide solution — Antagonistic actions of acids and alkalis on the 

 pulsations of the heart and of Desmodium — Similarities of reaction in 

 rhythmic tissues, animal and vegetal. 



We will now study the effects of various chemical agents 

 on the pulsating activity of the Desmodium leaflet. These 

 may be applied either externally or internally. As regards 

 external application, a liquid reagent may be applied 

 directly on the pulvinule ; gases and vapours, on the other 

 hand, are made to circulate in the plant-chamber. We may 

 secure internal application by forcing in the solution at the 

 cut end of the petiole, by means of hydrostatic pressure 

 (cf. fig. 141). 



The characteristic effects of different reagents are seen 

 exhibited in the induced change of period or of amplitude 

 of pulsation. Another noticeable effect often observed is 

 the transposition of the systolic or diastolic limit of pulsa- 

 tion. Certain agents may thus induce an arrest at systole, 

 others at diastole. 



The effect of a given agent may be modified by various 

 conditions, such as internal or external application, the 

 strength of the solution, and the duration of application. 



Thus the same agent which in a strong solution induces 

 depression, may in a very dilute solution cause an exaltation. 



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