384 SIR THOMAS R. ERASER AND MR ALISTER T. MACKENZIE ON 



Throughout the observations, the auricles contract and dilate regularly until finally the 

 ventricle becomes permanently small and pale in systole and resists the efforts of the 

 auricles to propel their contents into it. The auricles continue to contract after ventri- 

 cular standstill, and they respond to mechanical stimulation after the ventricle has 

 ceased to do so. 



With larger doses, the main features of the action are similar, viz. : slowing of the 

 heart, increased extent of the systolic and diastolic movements of the ventricle, the 

 tendency to predominance of diastole, the occurrence of diastolic pauses of irregular 

 length and at irregular intervals, and at last permanent systole of the ventricle, which 

 becomes very pale and rigid. The auricles are better filled and empty their contents 

 completely in the early stages, but later the ventricle does not contract rhythmically 

 with the auricles, and several auricular contractions precede each ventricular systole. 

 When the final systole of the ventricle occurs, the contractions of the auricle appear to 

 be unsuccessful in propelling the smallest portion of their contents into the ventricular 

 cavity. In the case of the largest doses which were applied to the surface of the heart 

 the course of events was similar in kind though different in degree. In the last experi- 

 ment described (Experiment LV.), the observations were discontinued when the dia- 

 stolic pause continued for 10 minutes or longer, though in other similar experiments it 

 was found that mechanical stimulation of the heart induced contractions of all its 

 chambers after the organ appeared to be finally arrested in diastole, and repeated irrita- 

 tion changed the type of arrest from diastolic to systolic. 



In several other experiments, with large doses of extract (not described), the first 

 noticeable change — increased completeness of the systolic movement of the ventricle — 

 became so marked that the heart was permanently arrested in systole within 30 minutes 

 of the application of the extract. In such cases, the ventricular cavity becomes quite 

 obliterated and the cardiac muscle immediately becomes acid in reaction. 



During the experiments, the laboratory temperature was from 15° C. to 18° C. 



Experiments afterwards described (heart perfusion) indicate how the quantity of 

 extract affects the nature of the changes produced in the heart. 



Influence of the Vagus. 



In order to determine if S. sarmentosus acts on the vagus, numerous experiments 

 were performed on the lines of those just described. With a laboratory temperature of 

 18° to 20° C, it was found that electrical stimulation of the exposed vagus nerve in the 

 frog caused complete arrest of the heart in extreme diastole for several seconds. Within 

 three minutes of the application of a solution in Ringer's solution of sulphate of atro- 

 pine to the surface of the heart, electrical stimulation of the vagus produced no effect. 

 When , 000025 gram of atropine sulphate was instilled within the pericardium, the 

 strongest stimulation (from a Du Bois Reymond's apparatus and a single bichromate 

 cell) of the isolated vagus nerve produced no effect on the heart during two hours, ex- 

 cepting acceleration in some instances. After this interval, electrical stimulation of the 



