PRODUCTION OF THE PULSE. 67 



in all the vessels at the same instant. Marey registered simultaneously the 

 impulse of the heart, the pulse of the aorta and the pulse of the femoral 

 artery, and ascertained 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 confirmed the views of 

 other physiologists, particularly Weber, who described this progressive retar- 

 dation of the pulse, 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 is known 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 charac- 

 ters of the pulse must be subject to great variations. Many of these may be 

 appreciated simply by the sense of touch. Writers treat of the soft and com- 

 pressible pulse, the hard pulse, the wiry pulse, the thready pulse etc., as indi- 

 cating various conditions of the circulatory system. The character of the 

 pulse, aside from its frequency, has always been regarded as of great impor- 

 tance in disease. 



Form of the Pulse. It is evident that few of the characters of a pulsa- 

 tion, 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, instruments for registering the 

 pulse have been constructed, with the view of analyzing 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, 



FIG. 24.Sphygmograph of Marey. 



The apparatus is securely fixed on the forearm, so that the spring under the screw V is directly over 

 the radial artery. The movements of the pulse are transmitted to the long and light wooden lever 

 L and registered upon the surface P, which is moved at a known rate by the clock-work H. The 

 apparatus is so adjusted that the movements of the vessel are accurately amplified and registered 

 by the extreme point of the lever. 



with one knee over the other, the beating of the popliteal artery will 

 produce marked movements of the foot. If a lever provided with a mark- 

 ing-point in contact with a slip of paper moving at a definite rate could be 

 applied to an artery, the point of the lever would register the movements of 



