EFFECT OF CHEMICAL AGENTS 341 



dilute NaHO solution (fig. 190), on the other hand, induces 

 exactly the opposite effect — namely, an arrest at systolic 

 contraction. 



Summary 



The effect of chemical reagent on the pulsating activity 

 of Desmodium is to a certain extent modified by the tonic 

 condition of the specimen. 



The effect is also dependent on the strength of the 

 reagent. Very dilute application often induces an effect 

 opposite to strong. 



Alcohol induces a transient exaltation followed by 

 depression. The period of pulsation is lengthened. 



Carbonic acid when dilute induces an exaltation of 

 amplitude, with prolongation of period of each pulsation. 

 Long application of undiluted gas induces an arrest : revival 

 takes place on substituting fresh air. 



Vapour of ether induces a temporary arrest of pulsation ; 

 the pulsation may be revived on blowing off the vapour. 



The effect of chloroform is similar to that of ether, but 

 its toxic effect is greater, any excess causing permanent 

 arrest. Diluted vapour causes a preliminary exaltation 

 followed by arrest. Revival may take place after quick 

 substitution of fresh air. 



Vapour of carbon disulphide applied for a short time 

 also induces a transient arrest. 



Copper sulphate solution when applied directly on the 

 pulvinule causes an almost immediate arrest. But when 

 applied at the cut end of petiole, the arrest does not take 

 place till the lapse of a period, required for the solution 

 to ascend to the motile organ. 



The poisonous reaction of potassium cyanide solution is 

 more powerful than that of copper sulphate. 



The effect of acids and alkalis on the rhythmic move- 

 ments of Desmodium are, as on the animal heart, antagonistic. 

 In both, acids induce a standstill in diastole, while alkalis 

 induce arrest in systole. 



