IIEMICAL REAGENTS ON AUTONOMOUS PULSATION 32 1 



water had thus produced an absolute displacement of the 

 mean position of the leaflet, of 1-5 mm. Considering these 

 facts, it becomes reasonable to regard the motile indications 

 of Desmodium as similar to those of Mimosa ; hence the 

 down position of the Desmodiurn leaflet may be regarded 

 as one of contraction, the up position being one of relaxation. 

 Thus in Desmodium the down position of the leaflet corre- 

 sponds to the systolic contraction, and the up position to the 

 diastolic expansion of the heart. 



Mode of application of chemical reagents. — Having 

 now to some extent determined the character of the move- 

 ments of the Desmodium 

 leaflet, we shall proceed 

 to observe in detail the 

 modification of their 

 movements by the action 

 of various chemical re- 

 agents. Three different 

 methods of application 

 may be employed. In 

 the first place, the chemi- 

 cal reagent may be dis- 

 solved in the water in 

 which the specimen is 

 placed. The solution will 

 thus reach the motile 



organ by the same process as that which brings about the 

 ascent of sap. The characteristic action of the chemical 

 reagent will be demonstrated in the subsequent modification 

 of the responses. 



This method of applying a reagent at one point — in this 

 instance the cut end of the petiole — and observing the sub- 

 sequent physiological effect on the distant motile organ, is of 

 special interest and importance in the case of poisons. For 

 it serves to elucidate the obscure question of the ascent of 

 sap through tissues that have been killed by poison (p. 385). 



In order to observe and compare the responses of the 



Y 



Fig. 129. Method of Application of 

 Chemical Agent to Cut End of Petiole 



