352 



PLANT RESPONSE 



(5) Antagonistic actions of acid and alkali. — But the most 

 remarkable of all the similarities seen in the pulsations of 

 rhythmic tissues of animal and vegetable, is that of the 

 antagonistic actions of acid and alkali. Acid induces in 

 the case of the heart a relaxed or diastolic standstill, whereas 



Fig. 153. Systolic Arrest of Heart-beat by Dilute NallO Solution (Gaskell) 



alkali induces an effect exactly the opposite, the standstill 

 being brought about at systolic contraction (figs. 152 and 1 53). 

 It is also known that the standstill caused by one of these 

 reagents can be counteracted by the antagonistic action of 

 the other. 



It is astonishing to find that exactly the same effects 

 are produced by these reagents on the tissue of Desmodium. 

 I first tried the effect of dilute hydro- 

 chloric acid, which, as will be seen, 

 produced an arrest of pulsation in 

 the 'diastolic' or relaxed position 

 (fig. 154). I next tried the effect 

 of alkali — dilute solution of sodium 

 hydrate — and it will be seen that this 

 produced an arrest of pulsation in 

 the ' systolic ' or contracted position 

 (fig. 155). In records of the effect of 

 this reagent on other specimens, in 

 which its action had not proceeded 

 so far, there was a continuous dimi- 

 nution of pulsation with a shifting 

 towards the systole ; and when an acid was now applied, 

 the antagonistic character of its action to alkali was clearly 

 shown, by a gradual revival of response, with a shifting 

 towards the diastole. In the present record, the systolic 

 standstill caused by alkali was allowed to proceed far, and 



FlG. 154. Arrest of Des- 

 modium Pulsation at 

 ' Diastole ' by Applica- 

 tion \ of Acid 



