426 Historical 



the more quickly does it move in the arteries, and the more easily 

 does the heart contract, since the blood pressure representing the 

 resistance opposed to the systole of the heart becomes weaker. It is 

 well known that every muscle contracts so much the more easily and 

 quickly, in proportion as the execution of this movement requires less 

 expenditure of energy. Consequently, in such a case, the arterial 

 expansion will take place in so much less time; and if the time from 

 the rise of the blood pressure to its maximum increase is very short, 

 that will be expressed in the steepness of the ascending line of the 

 curve; and if the period of time is so short that it cannot be measured, 

 then the line of ascent will appear completely vertical, as is almost 

 always the case in the normal state. 



When, on the contrary, on the tracings made in compressed air 

 we observe that the line of ascent is becoming oblique, we conclude 

 that the resistance opposed to the blood wave produced by the systole 

 of the heart has increased at the same time that the flow of blobd is 

 checked in the capillaries; that consequently the systole of the heart 

 is less rapid, that the blood wave reaches the arteries slowly, and 

 that consequently also the dilatation of the arteries does not take 

 place suddenly, but progressively. 



The apex of the curve which we do not wish to consider as a 

 mathematical point, but as the convergence of the ascending and 

 descending lines, shows us the moment when the artery, having 

 reached the maximum of its dilatation by the blood distending it, 

 resists by means of its own contractility the pressure of the blood 

 which acts upon it, and by its contraction exerts a new impulse on 

 the blood. 



If the resistance which the blood wave meets in the arterial 

 trunks at a distance from the heart decreases a little, then the flow 

 of the blood in the direction of the current, from the heart to the 

 periphery, becomes easy and rapid, and the pressure of the blood 

 in the arteries decreases rapidly, and the arteries can contract rapidly. 

 The more marked this tendency is, the more acute the apex of the 

 tracing appears, as we can see, for example, in the normal pulse. 



The contrary takes place in compressed air, and the original 

 acute angle changes, as we have seen, into a more or less obtuse angle, 

 and even into an arch, which takes place, if, on account of the con- 

 siderable obliquity of the line of ascent, the highest vertical point 

 intersects the middle of the curve. 



Consequently the increase of resistance already expressed in the 

 ascending part of the curve, by its obliquity under the influence of 

 the compressed air, is communicated or transmitted also to the apex 

 of the curve (p. 557-560) .... 



The descending wave of the curve of the pulse, which corresponds 

 to the diastole of the heart, shows us the decrease of the blood 

 pressure in the arteries, coinciding with the closing of the semilunar 

 valves, and with the simultaneous flow from the large arteries into 

 the capillaries, that is, the arteries gaining the victory in their struggle 

 against the pressure of the blood, and by means of their elasticity, 

 through the transformation of their expansive energy into active 

 energy, contracting to the minimum limit of their caliber. The vary- 



