1883.] 



Experiments upon the Heart of the Dog. 



273 



circulation of the blood to take place in a normal dog, based upon the 

 maximum quantity of blood sent out from the left heart at each 

 systole, as determined by our experiments, give results which agree 

 with what we would expect from the time found necessary by 

 Vierordt from direct experiment for the jugular-femoral path. 3. It 

 is probable that in our experiments the left heart, at the time the 

 maximum outflow was obtaiued from it, worked under conditions of 

 pressure closely resembling those to which it is subject during life. 

 The pressure in the left auricle, with the highest venous pressure 

 (46 millims. of mercury) used on the right side, had a maximum 

 value of 20 millims. of mercury, a mean value of 16 millims., which 

 is probably about what occurs during life, since Goltz and Gaule 

 found that the maximum pressure in the right auricle of the dog is 

 about 19'6 millims. of mercury. 



Owing to the difference in pulse-rate between the dog and man, no 

 inference can be made with any certainty from the results obtained 

 with the dog to the case of man. 



II. Influence of Variation of Arterial Pressure on the Work done by the 



Heart. 



Arterial pressure was varied by raising or lowering the end of the 

 outflow tube leading from the aorta. As the result of the experi- 

 ments we can state that variation of arterial pressure from 58 to 147 

 millims. of mercury, have practically no direct effect whatever upon 

 the quantity of blood sent out from the left ventricle at each systole. 



Since the pulse-rate is not altered, the work done by the left 

 ventricle, therefore, varies directly as the arterial pressure against 

 which it works, within the limits named. For how much wider limits 

 than those given this may hold true we have not yet determined. 

 Since there is every reason to believe that under normal conditions 

 the force of the systole is more than sufficient to completely empty 

 the ventricular cavity, and we have found that with arterial pressures 

 from 58 to 147 millims. the quantity of blood pumped out from the 

 left ventricle at each systole remains constant, it seems probable that 

 within these limits at least the force of the ventricular contraction is 

 not influenced by variation in arterial pressure, but remains maximal 

 throughout. 



III. Influence of Variation of Venous Pressure on the Work done by 



the Heart. 



The venous pressure on the right side was gradually increased 

 from 10 centims. to 60 or 70 centims., and the outflow from the aorta 

 measured for each venous pressure used. The records of these 

 experiments show in a marked manner the influence of venous 

 pressure on the outflow from the ventricle. As the general results of 



VOL. XXXV. T 



