PROOF OF INCREASED CARDIAC FORCE. 51 



still farther increased; but the reverse when the capillaries 

 were relaxed. But what would be the effect of increasing the 

 size of the wave of blood, the muscular power remaining the 

 same ? The increased quantity of blood would take longer to 

 be driven in, the oscillation would not be abrupt, and, in fact, 

 it would merely cause a higher mean tension. The increase of 

 the wave, along with the increase of force, would cause a similar 

 effect. 



Intermittence or slowness of the pulse would cause greater 

 oscillation, the long interval allowing the escape of more blood 

 from the capillaries ; the tension would fall much. From ths 

 length of the interval, the heart would have received more 

 blood than usual, and the succeeding wave would be larger ; but 

 there being more room for it m the arterial system, it would not 

 raise the maximum height of oscillation much, if at all, above 

 the normal. If the force of the heart were lessened, the oppo- 

 site results would take place, and the oscillations be less abrupt 

 and of smaller amplitude. 



Let us now see with which of all these conditions the effects 

 observed from digitalis agree. 



In experiment 6, a strong well-fed dog was operated on. At 

 3' 48" the respiration was 20, the pulse 84, the mean tension 

 5'65 inches of mercury, and the oscillation 5 — 6*5. A grain 

 of digitaline was then injected into the jugular vein. At 

 59' 45'' the mean tension is 5*7, or only -gL-th of an inch 

 higher, but the oscillation is now 4 — 8, or 4 inches instead of 

 IJ. This increase in oscillation we have seen can be due only 

 to slowness or intermittence of the pulse or increase of the 

 force of the cardiac contractions, as far at least as the circula- 

 tory apparatus is concerned, and that in the former case the 

 maximum would not be much above the normal, which in this 

 case it is ; and therefore we would consider as proved that the 

 force of the heart is increased, were it not that we observe the 

 remarkable decrease in the number of respirations, and are led 

 to inquire whether it is not to the greater influence of these, 

 rather than to any increase of the heart's force, that the oscilla- 

 tions are due ; and this indeed seems highly probable, as the 

 amount of oscillation is so great that we cannot easily imagine 



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