DR THOMAS R. FRASER ON" STROPHANTHUS HISPIDUS. 419 



cardiac muscle itself. It is directly acted upon by Strophanthus ; and the chief result of 

 the action is an increase of its contractility, rendering systole more prolonged and perfect. 



With a considerable or a large dose of Strophanthus, the systolic type of change is 

 produced, in which, by a direct action on the heart's muscle, the capability to relax is 

 diminished, until diastole becomes impossible, and the heart ceases to pulsate, with the 

 ventricle so thoroughly contracted that its cavity is almost effaced, and with the cardiac 

 muscle so profoundly modified that it passes at once into a state indistinguishable from 

 that of rigor mortis. The cardiac muscle appears, therefore, to be affected in the same 

 way as the skeletal muscles. 



While the production of the type of cardiac action distinguished as the systolic 

 admits of clear explanation, there is considerable difficulty in satisfactorily explaining the 

 production of the changes characterising the diastolic type. Being produced only by small 

 doses, this type has the special interest that it is representative of the changes which 

 must occur when Strophanthus is administered for therapeutic purposes. Even in the 

 extreme form of its production, the irritability and contractility of the heart are not 

 destroyed ; for, in experiments that have been described, during actual standstill of the 

 heart in extreme diastole, mechanical irritation nearly invariably caused a perfect contrac- 

 tion of the heart, and rhythmic contractions every now and then spontaneously occurred ; 

 while actual loss of contractility appeared only when the largely-dilated ventricle, after 

 a long period of suspended action, gradually lost its abnormal dilatation by slowly and 

 imperceptibly shrinking to normal or smaller than normal dimensions. 



The evidence afforded by the experiments in which the diastolic type of change 

 occurred notwithstanding the administration of atropine, appears to exclude stimulation 

 of any part of the cardio -inhibitory apparatus as the cause of its production. There 

 remain as possible explanations a direct action either on the muscle of the heart or on 

 the excito-motor nerve structures. 



The former explanation is improbable, as it implies that Strophanthus is capable in 

 small doses of exerting an action on muscle of a kind contrary to that which it 

 undoubtedly exerts in large doses. It is also contrary to evidence, for even in extreme 

 forms of the diastolic type of action, the contractions of the heart are strong, although 

 not rapid, and they are sufficient completely to empty the ventricle of the large volume 

 of blood which it had contained during its exceptionally dilated state. Further, no 

 experimental evidence has been obtained of a dilating action on muscle. 



In favour of a weakening of the excito-motor nerve structures are the circumstances 

 that such a weakening, combined with an increase of muscle contractility, would account 

 for the changes constituting the diastolic type of cardiac action ; that when the ventricle 

 is at rest in diastole, strong stimuli may cause it to contract, while gentle stimuli fail to 

 do so ; and that spontaneous contractions sometimes occur after several successive con- 

 tractions of the auricles have greatly distended the ventricle, although a single auricular 

 contraction does not interrupt the standstill of the ventricle in moderate diastole. 



At the same time, weakness of the excito-motor nerve structures alone would not 



