246 THE BODY AT WOKK 



Much may be learned from the pulse with regard to the con- 

 dition of the vascular system, although it is impossible to 

 balance the effects of the several factors which go to the 

 production of its various modifications. The character of the 

 pulse depends upon the vigour with which the heart is beating, 

 the efficiency or otherwise of the cardiac valves, the quantity 

 of blood in circulation, the suppleness of the arterial walls, the 

 degree to which they are contracted, the resistance offered by 

 the smaller vessels. Departures from the normal may take 

 the direction of unduly high tension or of unduly low tension. 

 In place of the sudden rise and more or less gradual fall, with 

 the slightest possible roughness due to secondary waves, which 

 constitutes a healthy pulse, the rise may be shorter, its sub- 

 sidence prolonged. This is a high-tension or hard pulse. 

 The pressure in the arteries is unduly high, or the walls of the 

 vessels are not as elastic as they should be. Considerable 

 pressure is needed to obliterate such a pulse i.e., to prevent it 

 from passing on beneath the finger. As the converse of this 

 condition, the difference between the beginning of the pulse and 

 its end may be very marked, the vessel suddenly dilating and 

 as suddenly collapsing. But little pressure is needed to stop 

 such a low-tension pulse from passing beneath the finger. 

 Usually it has a distinct secondary or dicrotic wave. Some 

 tactile education is needed by the finger that aspires to read 

 the pulse. It was hoped that the personal equation would be 

 of less importance if mechanical records were substituted 

 for statements as to the impression produced upon the 

 observer. Various forms of sphygmograph (o-^uy/^o?, pulse) 

 have been invented for this purpose. The form commonly used 

 (Fig. 14) consists of a metal spring which is adjusted so that a 

 button beneath its free end presses on the radial artery at the 

 wrist. The force with which it presses is regulated by a screw. 

 At each pulsation its free end is lifted by the distension and 

 rounding of the artery. Its movement is transmitted by 

 means of a continuous screw, attached to it vertically, to a 

 cogged wheel, which in its turn raises a lever. The end of the 

 lever scratches blackened paper fastened on a plate moved by 

 clockwork. Records made in this way are useful for future 

 reference. They are not, however, so valuable as it was 

 anticipated that they would be. The form of the tracing 



