EFFECT OF CHEMICAL AGENTS 



339 



more pronounced than that induced by copper sulphate. 

 The poisonous action of cyanide is equally powerful in 

 abolishing the rhythmic activity of the Desmodium leaflet. 



Fig. i 86. — Quick arrest of pulsation at systole by 

 the action of KCN solution. 



This is well observed in fig. 186, where the pulsation is 

 seen to be quickly arrested at systole. 



Antagonistic Actions of Acid and Alkali 



We have hitherto seen the remarkable similarities of the 

 effect of various chemical agents on the rhythmic activi- 

 ties of the animal and vegetal tissues. A very striking 



Fig. 187. — Arrest of pulsation of the heart of frog in diastole by the action 

 of dilute lactic acid. (Gaskell.) Record to be read from right to left 

 in this and following figures. 



characteristic is the antagonistic reactions of acid and alkali 

 on the animal heart. Application of very dilute acid 

 induces in the heart an atonic reaction, in consequence of 

 which there is induced an arrest of pulsation in the relaxed 

 or diastolic condition (fig. 187) . The action of dilute alkaline 



