418 DR THOMAS R. FRASER ON STROPHANTHUS HISPIDUS. 



anthuSj have therefore shown that the production by relatively large doses of Strophanthus 

 of increase of ventricular systole and of standstill of the heart, with the ventricle pale and 

 strongly contracted, cannot be prevented by atropine. Contrary to expectation, they 

 have also, however, shown that paralysis of the cardio-inhibitory branches of the vagus by 

 atropine cannot prevent relatively small doses of Strophanthus from producing slowing of 

 the heart by prolongation of ventricular diastole, and even from producing standstill of the 

 ventricle in a condition of extreme diastolic enlargement. At the same time, it has been 

 found that these results of small doses of Strophanthus are more difficult to be obtained 

 when atropine is also administered ; but this difficulty may be explained by the removal, 

 as a result of the administration of atropine, of the normal and continuously operating 

 influence of inhibition, which, when present, aids the action of small doses of Strophanthus 

 in producing exaggeration of diastole. As the diastolic type of action may also occur 

 after distraction of the brain and medulla, it is, therefore, indicated that the exaggeration 

 of ventricular diastole, which is caused by Strophanthus, is not the result of stimulation 

 of any part of the vagus cardio-inhibitory apparatus. 



At the same time, as the following experiment shows, the inhibitory power of the 

 vagus over the heart is not paralysed by Strophanthus, during the time in which profound 

 changes in the heart's action are being produced by it. 



Experiment CXXIII. — In a pithed frog, the heart was exposed and the trunks of the 

 vagi nerves were dissected and isolated. The minimal current from a Du Bois induction 

 coil and a Daniell's cell, capable of arresting the heart's contractions, was that obtained 

 with the secondary at 90 mm. After the several stimulations of the vagus required to 

 determine this minimal, the contractions of the heart became slow and feeble, the rate 

 being only 6 per 30 sec. 



One minim of a solution of 0'05 grain of strophanthin in 100 minims of water 

 ( = 0*0005 grain) was placed upon the heart's surface. The contractions soon after- 

 wards became irregular, and occasionally they ceased for several seconds at a time, 

 with the ventricle in extreme diastole. In 12 min., in 15 min., and in 40 min. after the 

 application of Strophanthus, the minimal current that produced cardiac standstill was 

 90 mm. ; but in 57 min. it was 80 mm. After the last stimulation, the pauses of the 

 ventricle in extreme diastole became so prolonged and so irregular in occurrence, that 

 trustworthy results could no longer be obtained. 



Further evidence of the retention by the vagi of their cardio-inhibitory function 

 during the action of Strophanthus, will be adduced in the - description of experiments on 

 the circulation in rabbits. 



Summary of Examination of Structures involved, and Nature of Involvement, in the 

 Production of the Changes in the Heart's Action. 



The consideration of the structures affected, and of the pharmacological change 

 produced upon them, has rendered it very apparent that one of the structures is the 



