134 



INSTRUMENTS FOR INVESTIGATING THE PULSE. 



Poiseuille's Box-sphygmometer. The exposed artery (Fig. 41, a a) is en- 

 closed for a distance in its continuity in an oblong box (K K) , filled with some 

 indifferent fluid. There communicates with the interior of the box a graduated 

 vertical tube (b), filled to a certain point, in which the fluid rises and falls, 

 in accordance with the quantity of blood contained in the artery. The box is 

 constructed like an ordinary box, one half representing the body and the other 

 half the lid. A circular opening is made in each end of the box, one half being 

 contributed by the body and the other half by the lid, in which the artery 

 is hermetically sealed by means of soft fat. Poiseuille found the distention of 

 the carotid during diastole in the horse to be equal to ^, and in the dog to 

 ^ of the entire volume of the arterial segment. The instrument does not record 

 any more minute details in regard to the movement of the artery during the 

 phases of the pulse. 



Herisson's Tubular Sphygmometer (Fig. 42) consists of a glass tube closed at 

 its lower extremity by an elastic membrane and filled to a certain level with 

 mercury. The apparatus is placed vertically on the skin over a pulsating artery, 

 the beats of which set the column of mercury in motion. A similar instrument 



FIG. 41. Poiseuille's Box-cabinet Sphygmometer: a a, the exposed artery; 

 K K, the surrounding box with the vertical tube and scale b. 



FIG. 42. The Tubular 

 Sphygmometer of 

 Herisson and Chelius. 



was used in 1850 by Chelius, who succeeded with its aid in discovering the double 

 beat of the normal pulse. "After it (the mercury) has been raised by the impact 

 of the blood-wave, it falls again as suddenly to its lowest level, after first making 

 another short pause at some intermediate point." 



Marey's Sphygmo graph is based on a combination of the lever (which was first 

 employed by Vierordt in 1855 m the construction of his "sphygmograph") with 

 an elastic spring (Fig. 43, A). The latter, which is screwed fast at one extremity 

 (z) , while the other extremity is free and provided with a round pad (y) , presses 

 against the radial artery with a force equal to that of the spring. To the upper 

 part of the pad is fixed a short vertical ratchet (k) , which, when acted upon by 

 a weak spring (e) , turns a small cogwheel (t) , from the axis of which a light 

 wooden lever (v) extends almost horizontally. This writing lever is provided at 

 its outer extremity with a delicate point (s) , which records the movements of 

 the pulse on the smoked surface of a plate (P) made by clockwork (u) to pass in 

 front of the point of the writing lever at a uniform rate. Marey's instrument is 

 trustworthy and is quite extensively used. 



Marey's sphygmograph is adapted solely for the radial pulse. It is placed 



