ORIGIN AND CHARACTERISTICS OF THE ELASTIC ELEVATIONS. 139 



curve, the further the artery experimented upon is distant from the 

 heart (Landois, 1863). Compare the curves, Fig. 54, p. 134. 



The shortest accessible course is that of the carotid : where the dicrotic wave 

 reaches its maximum 0*35 to 0*37 sec. after the beginning of the pulse. In the 

 upper extremity the apex of the dicrotic wave is 0'36 to 0*38 to 0'40 sec. after 

 the beginning of the pulse-beat. The longest course is that of the arteries of the 

 lower extremity. The apex of the dicrotic wave occurs 0*45 to 0*52 to 0'59 sec. 

 after the base of the curve. It varies with the height of the individual. 



(2.) The dicrotic elevation in the descent is lower (Naumann), and 

 is less distinct (Landois), the further the artery is situated from the 

 heart. This is just what one would expect viz., the longer the 

 distance which the wave has to travel the less distinct it must become. 



(3). It is more pronounced in a pulse where the primary pulse-wave 

 is short and energetic (Marey, Landois). It is greatest relatively 

 when the systole of the heart is short and energetic. 



(4.) It is greater the lower the tension or pressure of the blood 

 within the arteries (Marey, Landois), [and is best developed in a soft 

 pulse]. In Fig. 58, IX and X were obtained when the tension of the 

 arterial wall was low; V and VI, medium; and VII with high tension. 



Conditions Influencing Arterial Tension. It is diminished at the beginning 

 of inspiration, by haemorrhage, stoppage of the heart, heat, an elevated position of 

 parts of the body ; it is increased at the beginning of expiration by accelerated 

 action of the heart, stimulation of vaso-motor nerves, diminished outflow of blood 

 at the periphery, and by inflammatory congestion (Knecht) ; further, by certain 

 poisons, as lead, amyl nitrite ; compression of other large arterial trunks, action of 

 cold and electricity on the small cutaneous vessels, and by impeded outflow of venous 

 blood. When a large arterial trunk is exposed the stimulation of the air causes 

 it to contract, resulting in an increased tension within the vessel. In many 

 diseased conditions the arterial tension is greatly increased [e.g., in Blight's 

 disease, where the kidney is contracted ("granular"), and where the left ventricle 

 is hypertrophied]. 



In all these conditions increased arterial tension is indicated by the dicrotic 

 wave being less high and less distinct, while with diminished arterial tension it is 

 a larger and apparently more independent elevation. Moens has shown that the 

 time between the primary elevation and the dicrotic wave increases with increase 

 in the diameter of the tube, with diminution of its thickness, and when it 

 coefficient of elasticity diminishes. 



II. Origin and Characteristics of the Elastic 

 Elevations. 



Besides the dicrotic wave, a number of small less-marked elevations 

 occur in the course of the descent in a sphygmogram (Fig. 58, e, e). 

 These elevations are caused by the elastic tube being thrown into 

 vibrations by the rapid energetic pulse-wave, just as an elastic mem- 

 brane vibrates when it is suddenly stretched. The artery also executes 



