INSTRUMENTS FOR INVESTIGATING THE PULSE. 137 



most complete instrument and the one whose curves most closely correspond with 

 the pressure-variations actually taking place in the artery is that in which the 

 resistance within the apparatus itself is reduced to a minimum, in which those 

 parts that execute the largest movements are as light as possible, but in which 

 the bulk of that portion of the instrument that is directly set in motion by the 

 movement of the blood in the artery, is strong enough and heavy" enough for its 

 equilibrium to be but slightly disturbed by even considerable force. 



Useful sphygmographs have been described by other investigators, as Nau- 

 mann, Frey, and others. For practical purposes Dudgeon's instrument, which is 

 easily manipulated, may be recommended; 



the load is applied by the pressure of a spring, . 



or, better, by a weight and beam, and the 

 tablet moves horizontally. A system of lines 

 is recorded together with the curve, making it 

 possible to determine by measurement the size 

 and chronological development of the pulse- 

 beats. 



Nomenclature of Pulse-tracings. In every 

 pulse-tracing (sphygmogram or arterio- 

 gram) there are distinguishable the as- 

 cending limb, the apex, and the descend- 

 ing limb. Irregular elevations in the course 

 of the descending limb are called catacrotic 

 elevations, while those in the ascending limb 

 are known as anacrotic elevations. The de- 

 scending limb almost always contains sec- 

 ondary elevations, while the" ascending limb 

 almost always appears as a simple rising 

 line. When a recoil-elevation, which will be 

 described more fully later on, occurs once or FlG> 46. Dudgeon's Sphygmograph. 



twice in the descending limb, the sphygmo- 



graphic curve is called dicrotic or tricrotic. When, as happens if the pulse- 

 beats follow one another in rapid succession, the succeeding beat cuts off the 

 recoil-elevation of the preceding curve, the curve is called monocrotic. 



Method of Making Sphygmographic Tracings. The tracings are recorded on 

 smooth glazed paper like that used for visiting cards, which has been covered with 

 a delicate translucent layer of soot by exposure over burning camphor or a 

 smoking lamp. The tracing is fixed by immersing the paper in a solution of 

 shellac and alcohol, after which it is allowed to dry. 



Mensuration of Sphygmographic Tracings. When a tablet is made to move 

 at a uniform rate by means of clockwork, the vertical height and horizontal 

 length of individual portions of the tracing can be measured with a fine rule. 

 The distance traversed by the tablet in a second being known, it is possible by 

 actual measurement to compute the duration of the individual portions of the 

 pulse-movement. Accurate measurements of this kind must be made under the 

 microscope with the aid of an ocular micrometer, a low magnification and direct 

 illumination being employed. The sections to be measured are placed be- 

 tween two lines that, in the case of sphygmographs like Marey's, which make 

 a curved tracing, must be arcs of a circle (of which the writing lever is the 

 radius) , and in the case of the angiograph must be vertical. 



An especially convenient method consists in recording the curve on a 

 tablet attached to one end of a vibrating tuning-fork (Fig. 60). Another less 

 accurate method consists in recording the vibrations of a tuning-fork on the tablet 

 of the sphygmograph at the same time that a Sphygmographic tracing is being 

 recorded, the latter being above the tuning-fork record. 



The Gas-sphygmoscope. To meet the objection that has frequently been urged 

 against instruments for registering the pulse, namely that the secondary elevations 

 observed in the sphygmogram are due to the after- vibrations of the apparatus 

 from inertia, Landois constructed a gas-sphygmoscope, in which the movement of 

 solid bodies is excluded and any after-vibration of inert masses that have been 

 set in motion is, therefore, impossible. 



The superficial arteries, whose movement is communicated to the overlying 

 skin, will, naturally, through the movement imparted to this layer of the skin, 

 cause also a movement in the contiguous layers of air. The thin layer of air 

 above the pulsating cutaneous area (Fig. 48) a is excluded by means of a shallow 



