CHEMICAL REAGENTS ON AUTONOMOUS PULSATION 323 



tory exaltation of the amplitude of oscillation, which was 

 doubled, though at the same time the rhythm became slowed. 

 After ten minutes, however, these pulsatory movements grew 

 irregular and depressed, and the plant succumbed to the 

 action of the toxic agent, its pulsation undergoing complete 

 arrest forty-five minutes after application. In the case of a 

 weakly specimen, again, on filling the chamber with an 

 atmosphere of carbonic acid gas, the pulsations soon come to 

 a stop, and unless fresh air be quickly introduced, this arrest 

 becomes permanent. But with a vigorous specimen, the depres- 

 sion produced by this gas is very slow, and the permanent 

 arrest does not take place till after a considerable lapse of time. 



The effect of an agent, again, depends on the strength 

 of the solution, and the duration of application. A solution 

 which, in larger quantities, would produce depression, will 

 often, if given in very diluted form, cause the exaltation of 

 response. The sudden introduction of an agent which may 

 ultimately produce arrest, may act as a transitory stimulus, 

 bringing about a preliminary augmentation of response, to be 

 followed later by depression and arrest. The application of a 

 deleterious substance, again, for a short time, will cause a 

 temporary depression, from which there is revival ; but too 

 long-continued action of the same reagent will cause 

 permanent arrest. Besides all these, there is the interesting 

 phenomenon of accommodation, by which the plant becomes 

 gradually accustomed to the action of any adverse circum- 

 stance, and is thus rendered immune. 



Effect of anaesthetics. — Taking a specimen of Desmo- 

 diiun, I passed ether-vapour into the plant chamber. The 

 pulsatory movement which had hitherto been fairly uniform 

 now showed a transitory exaltation, and then fell with 

 remarkable regularity of decrement. The response next 

 showed an equally regular tendency towards the gradual 

 recovery of its previous amplitude, but with longer period, 

 this being protracted, from the normal two to four minutes. 

 Finally, the pulsation of this specimen was abolished, the 

 leaflet remaining in a position of relative relaxation, thirty 



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