136 



INSTRUMENTS FOR INVESTIGATING THE PULSE. 



bulging upward of the membrane of each of the upper cups, the movements of 

 which are propagated to the writing levers. 



The instrument sketched in Fig. 44 shows the entire registering apparatus 

 in duplicate. An instrument of this kind may, therefore, be placed with the two 

 pads on two different arteries; for example, when it is desired to demonstrate that 

 the pulse occurs earlier in the arteries near the heart than in more distant vessels. 



Although the instruments described are convenient to handle, it has been 

 found by experience that sudden variations in pressure are not accurately recorded 

 in consequence of vibration of the instrument itself; while when the variations 

 in pressure are less sudden, the records may under certain circumstances be fairly 

 accurate. Another disadvantage is that the movement of the writing lever Z is 

 not entirely synchronous with that of the button p. For this reason instruments 

 constructed on this principle are not well adapted for accurate time work. The 

 entire apparatus may also be filled with water, in which event leaden pipes are 

 used instead of the connecting rubber tubes. Thus adapted, the apparatus is 

 more accurate for slower movements, while a pneumatic instrument is better 

 adapted for rapidly varying phases, such as are presented by the movements of 

 the pulse. 



Landois 1 Angiograph. From one extremity of a plate (Fig. 45, G G) serving 

 as a base, arises a pair of arms, between the upper parts of which the lever (d r) 

 moves freely between two points. The long arm of this lever is provided with a 

 pad (e), directed downward, which is to be applied to the pulse. The short arm of 

 the lever on the other side carries a counter-weight (d) , heavy enough to maintain 



FIG. 45. Landois' Angiograph Represented Diagrammatically. In order to shorten the figure 

 a piece has been cut out of the writing lever. 



the entire lever in equilibrium. The extremity (r) carries a spring-ratchet, which 

 presses against a cogwheel. The latter is immovably fixed to the axis of the 

 light writing lever c f, which is also suspended between points and is supported 

 by the two uprights q and attached to the opposite end of the base G G. The 

 writing lever also is maintained in perfect equilibrium by means of a small counter- 

 weight. The needle k is suspended from the extremity of the writing lever 1, 

 where it is secured by a hinge and is readily movable; it is carried by its own 

 weight toward the tablet (shown in the figure in profile) , and as it moves up and 

 down it records the curve with a slight scratching movement on the delicately 

 smoked surface of the tablet. 



The lever d r at a point approximately opposite the juncture with the pad e 

 supports on the end of a vertical rod the flat plate q for the reception of weights 

 to increase the load on the pulse. The advantages of the instrument are : (i) The 

 load can be varied at will and can be accurately determined (while in Marey's 

 sphygmograph the pressure of the spring increases as the lever is raised) ; (2) 

 although the needle is constantly in contact with the smoked surface, it never- 

 theless records with a minimum degree of friction; (3) the movement of the 

 writing lever is a vertical up-and-down movement and not a curved movement 

 as in Marey's apparatus, thus considerably facilitating an accurate study and 

 measurement of the curves. In the construction of his sphygmograph Sommer- 

 brodt adopted the improvements embodied in Landois' angiograph. 



In the choice of a sphygmograph the guiding principle should be that the 



