FORM OF THE PULSE. 71 



which can readily be compressed against the bone. In an artery imbedded in soft parts 

 which yield to pressure, the actual dilatation of the vessel being very slight, pulsation is 

 felt with difficulty, if at all. "When obstruction of an artery is complete, as in ligation of 

 a vessel, the pulsation above the point of ligature is very marked and can be readily ap- 

 preciated by the eye. The explanation of this exaggeration of the movement is the fol- 

 lowing: Normally, the blood passes freely through the arteries and produces, in the 

 smaller vessels, very little movement or dilatation ; when, however, the current is ob- 

 structed, as by ligation or even compression with the finger, the force of the heart is not sent 

 through the vessel to the periphery but is arrested and therefore becomes more marked 

 and easily appreciated. In vessels which have become undilatable and incompressible 

 from calcareous deposits, the pulse cannot be felt. The character of the pulse indicates, 

 to a certain extent, the condition of the heart and vessels. We have spoken, when treat- 

 ing of the heart, of the varying rapidity of the pulse, as it is a record of the rapidity of 

 the action of this organ ; but it remains for us to consider the mechanism of its produc- 

 tion and its various characters. 



Under ordinary circumstances, the pulse may be felt in all arteries which are ex- 

 posed to investigation ; and, as it is due to the movement of the blood in the vessels, the 

 prime cause of its production is the contraction of the left ventricle. The experiments 

 of Marey have shown that the impulse given to the blood by the heart is not felt in all 

 the vessels at the same instant. By ingenious contrivances, which will be described 

 farther on, this observer has succeeded in registering simultaneously the impulse of the 

 heart, the pulse of the aorta, and the pulse of the femoral artery. He has thus ascer- 

 tained that the contraction of the ventricle is anterior, in point of time, to the pulsation 

 of the aorta, and that the pulsation of the aorta precedes the pulse in the femoral. This 

 only confirms the views of other physiologists, particularly Weber, who described this 

 progressive retardation of the pulse as we recede from the heart, estimating the difference 

 between the ventricular systole and the pulsation of the artery in the foot at one-seventh 

 of a second. 



It is evident from what we know of the variations which occur in the force of the 

 heart's action, the quantity of blood in the vessels, and from the changes which may 

 take place in the caliber of the arteries, that the characters of the pulse must be subject 

 to numerous variations. Many of these may be appreciated simply by the sense of touch. 

 We find writers treating of the soft and compressible pulse, the hard pulse, the wiry 

 pulse, the thready pulse, etc., as indicating various conditions of the circulatory system. 

 The character of the pulse, aside from its frequency, has always been regarded as of great 

 importance in disease ; and the variations which occur in health form a most interesting 

 subject for physiological inquiry. 



Form of the Pulse. It is evident that few of the characters of a pulsation, occupying 

 as it does but one-seventieth part of a minute, can be ascertained by the sense of touch 

 alone. This fact has been appreciated by physiologists ; and, within the last few years, 

 in order to accurately study this important subject, instruments for registering the pulse 

 have been constructed, to enable us to analyze the dilatation and movements of the 

 vessels. The idea of such an instrument was probably suggested by the following 

 simple observation : When the legs are crossed, with one knee over the other, the beating 

 of the popliteal artery will produce a marked movement in the foot. If we could apply 

 to an artery a lever provided with a marking point in contact with a slip of paper moving 

 at a definite rate, this point would register the movements of the vessel and its changes 

 in caliber. The first physiologist who put this in practice was Vierordt, who constructed 

 quite a complex instrument, so arranged that the impulse from an accessible artery, like 

 the radial, was conveyed to a lever, which marked the movement upon a revolving 

 cylinder of paper. This instrument was called a " sphygmograph." The traces made by 

 it were perfectly regular and simply marked the extremes of dilatation, exaggerated, of 



