288 PHYSIOLOGY. 



The time comprised between the beginning of the contraction of 

 the ventricle and the moment of the elevation of the sigmoid valves, 

 sometimes called the pre-sphygmic interval, 0.04-0.07 second, makes 

 the first element in the retardation of the pulse-wave in the beginning 

 of a cardiac pulsation. The second element in retarding the pulse is 

 the rate of the spreading of the pulse-wave in the arterial system. 

 The rate of the spreading of the pulse-wave is about 30 feet per 

 second, which is very different from the rapidity of the current of blood, 

 which is about 12 inches per second. The rapidity of the ventricular 

 wave varies as the force of the heart, and inversely is proportional to 

 the resistance of the orifices and to the arterial tensions. When 

 a systole of the heart is revealed by a beating of the radial artery, there 

 is not, at that moment, under one's finger a single drop of the blood 

 thrown off by the last systole. The pulse may be compared to a wave 

 produced by throwing a stone into the pond. 



The three factors concerned in the production of the pulse are: 

 (1) the action of the heart, (2) the elasticity of the large vessels, and 

 (3) the resistance of the smaller arteries and the capillaries. 



The pulse is really a shock, perceptible to the touch at each in- 

 crease of the arterial tension, and produced by successive affluxes of 

 the blood which the heart throws off. 



In order to perceive that shock, the vessel must be pressed by the 

 finger so as to make it lose its cylindrical form at that point. By 

 reason of the dilatation of the vessel, the finger is raised at that point. 

 That is, one perceives the pulse. As there may exist various changes 

 in the arterial tension, so there may be various types of pulse. Vari- 

 ations are, for the most part, pathological, and so may be considered 

 to be outside of the domain of physiology. 



When the physician feels the patient's pulse he gains valuable 

 information as to the condition of the heart and vessels. The exami- 

 nation of the characters of the pulse is usually confined to that por- 

 tion of the radial artery which lies in the wrist. Here the artery is 

 covered only by skin and subcutaneous tissue, while in addition the 

 shaft of the radius forms a bony support against which the artery may 

 be compressed by the fingers. From the pulse are noted the following 

 points : Force, rate and fullness. 



While such main features of the pulse were able to be depicted 

 by experienced finger-tips, it was felt that there was still very much 

 that the pulse would tell could it -be translated. 



Everyone has seen the movements produced in a limb by reason 

 of the pulsations of the popliteal artery, when one leg is kept crossed 



