MAYER'S GAS-SPHYGMOSCOPE. 



IOI 



and varied ; the writing-lever moves vertically, and not in a curve as in Marey's apparatus, 

 which greatly facilitates the measuring of the curves (fig. 77). 



Other sphygmographs are used, both in this country and abroad, including that of Sommer- 

 brodt, which is a complicated form of Marey's sphygmograph, and those of Pond and Mach. 



In every pulse-curve sphygmogram or arteriogram we can distinguish the 

 ascending part (ascent) of the curve, the apex, and the descending part (descent). 

 Secondary elevations scarcely ever occur in 

 the ascent, which is usually represented by a 

 straight line, while they are always present 

 in the descent. Such elevations occurring in 

 the descent are called catacrotic, and those 

 in the ascent, anacrotic. When the recoil 

 elevation or dicrotic wave occurs in a well- 

 marked form in the descent, the pulse is said 

 to be dicrotic, and when it occurs twice, 

 tricrotic. 



Measuring Pulse-Curves. If the smoked surface Fig. 78. 



on which the tracing is inscribed is moved at a uni- formal pulse-curve of the radial artery, 

 form rate by means of the clock-work, then the obtained by the angiograph writing upon 

 height and length of the curve are measured by a p i a t e attached to a vibrating tuning- 

 means of an ordinary rule. If we know the rate at f or k. Each double vibration = '01613 

 which the paper was moved, then it is easy to calcu- sec . 

 late the duration of any event in the curve. 



The curve may be recorded on a plate of glass fixed to a tuning-fork kept in vibration. Every 

 part of the curve shows little elevations (whose rate of vibration is known beforehand). All 

 that is required is to count the number of vibrations in order 

 to ascertain the duration of any part of the curve (fig. 78). 



G-as-Sphygmoscope. A small metallic or glass capsule (fig. 

 79), provided with an inlet and an outlet tube, and closed 

 below by a fine membrane, is placed over an artery. The 

 inlet tube is connected to a gas supply, and the outlet to a 

 rat-tailed gas-burner (b). The gas-jet responds to every pulse- 

 beat. Czermak photographed a beam of light set in motion 

 by the movements of the pulse. 



Haemautography. Expose a large artery of an animal, and 

 divide it so that the stream of blood issuing from it strikes 

 against a piece of paper drawn in front of the blood-stream. 



Fig. 80. 

 Hremautographic curve of the poste- 

 rior tibial artery of a dog. P, prim- 

 Fig. 79. ary pulse-wave ; ft., dicrotic wave ; 

 Gas-sphygmoscope of S. Mayer. .* c, e, elevations due to elasticity. 

 The curve so obtained (fig. 80) shows, in addition to the primary wave, P, a distinct dicrotic 

 wave, R, and slight vibrations, e, e, due to the variations in the elasticity of the arterial wall, 

 which shows that the movements occur in the blood itself, and are communicated as waves to 

 the arterial wall. By estimating the amount of blood in the various parts of the curve, we obtain 

 a knowledge of the amount of blood discharged by the divided artery during the systole and 

 diastole (i.e., the narrowing and dilatation) of the artery the ratio is 7: 10. Thus in the 

 unit of time, during arterial dilatation, rather more than twice as much blood flows out as 

 compared with what occurs during arterial contraction. 



