BY DR. BURDON-S ANDERSON. 225 



36. The Spring Kymograph. If we desire to obtain a 

 record of the complicated succession of variations of arterial 

 pressure which constitute an act of pulsation, precisely as 

 they occur as regards order, duration, and degree, or of the 

 exact interval of time between the close of one arterial expan- 

 sion and the commencement of the next, the instrument with 

 which we write must be of such a nature that it shall transmit 

 the movements communicated to it without mixing with them 

 any movements of its own. The most perfect of such instru- 

 ments is the so-called Federkymograpkion of Professor Fick. 

 The construction of the instrument will be readily understood 

 with the aid of Fig. 205. It consists essentially of a C-shaped 

 hollow spring of thin metal. The cavity of the spring is filled 

 with spirits of wine, and communicates with the artery by means 

 of a connecting-tube containing bicarbonate of soda. As the 

 pressure increases, the crescentic spring tends to straighten, 

 and vice versa. Hence, if the proximal end is fixed, the distal 

 end performs movements which follow exactly the variations 

 of arterial tension. These movements are of very small ex- 

 tent, but they are so exact that the slightest and most transi- 

 tory variations are expressed by them. Before they are writ- 

 ten on the cylinder they must be enlarged by a lever. 



It is not necessary to make any remarks as to the mode of 

 connecting the spring k3 r mograph with an artery, the modus 

 operandi being the same as that described in 34. It is, how- 

 ever, to be noted, that if it is intended to use the tracing ob- 

 tained by it for the purpose of determining the absolute arte- 

 rial pressure, the instrument must be first graduated by com- 

 parison with a mercurial manometer. This is effected as 

 follows : The kymograph being placed so as to write on the 

 recording cylinder, its artery tube, which communicates by a 

 side opening with a pressure bottle, is united with the proxi- 

 mal arm of the manometer. The pressure bottle is first 

 lowered until the liquid it contains stands at the same level 

 as the mercuiy in the proximal arm. A tracing is made on 

 the cylinder, which is the abscissa. The bottle is then raised 

 till the distal mercurial column is ten millimetres higher than 

 the proximal, and a second tracing taken, and so on at suc- 

 cessive increments of 10 mill, pressure, up to 150 mill, or 

 more. Bj r measuring vertically the distances in millimetres 

 between the horizontal lines so traced and the abscissa, a 

 series of results are obtained which express the values of the 

 ordinates of the tracing in millimetres of mercurial pressure. 



In tracings obtained by the spring kymograph it is seen 

 that the ascent of the lever, whi< >l Corresponds to the period 

 during which the artery is act^i on by the contracting ven- 

 tricle, is abrupt indeed, nearly vertical ; that towards the 

 vertex the tracing changes direction, gradually approaching 

 15 



