CIRCULATION. 381 



the successive up-and-down movements of the mercury would no longer be 

 marked over and over again in the same place so as to produce a single ver- 

 tical line. The space and time taken up by each fluctuation would be graph- 

 ically recorded in the form of a curve, itself a portion of a continuous trace 

 marked by the successive fluctuations ; thus both the respiratory and cardiac 

 fluctuations could be registered throughout an observation by a single complex 

 curving line. Ludwig stretched his paper around a vertical hollow cylinder 

 of brass, made to revolve at a regular known rate by means of clock-work, 

 and the conditions above indicated were satisfied l (see Fig. 100). Upon the 

 surface of such a cylinder vertical distance represents space, and a vertical line 

 of measurement is called, by an application of the language of mathematics, 

 an " ordinate ; " horizontal distance represents time, and a horizontal line of 

 measurement is called an " abscissa." The curve marked by the events re- 

 corded is always a mixed record of space and time. The instrument itself, 

 the essential part of which is the regularly revolving cylinder, is called the 

 " kymograph." 2 It has undergone many changes, and many varieties of it 

 are in use. Any motor may be used to drive the cylinder, provided that the 

 speed of the latter be uniform and suitable. 



The curve written by the manometer or other recording instrument may 

 either be marked upon paper with ink, as in Ludwig's earliest work ; or may 

 be marked with a needle or some other fine pointed thing upon paper black- 



p 



B L 



FIG. 101. The trace of arterial blood-pressure from a dog anaesthetized with morphia and ether. The 

 cannula was in the proximal stump of the common carotid artery. The curve is to be read from left 

 to right. 



P, the pressure-trace written by the recording mercurial manometer ; 



B L, the base-line or abscissa, representing the pressure of the atmosphere. The distance between 

 the base-line and the pressure-curve varies, in the original trace, between 62 and 77 millimeters, there- 

 fore the pressure varies between 124 and 154 millimeters of mercury, less a small correction for the 

 weight of the sodium-carbonate solution ; 



T, the time-trace, made up of intervals of two seconds each, and written by an electro-mag- 

 netic chronograph. 



ened with soot over a flame. The trace written upon smoked paper is the 

 more delicate. After the trace has been written, the smoked paper is removed 

 from the kymograph and passed through a pan of shellac varnish. This 



1 C. Ludwig: "Beitrage zur Kenntniss des Einflusses der Kespirationsbewegungen auf 

 den Blutlauf im Aortensysteme," Mailer's Archiv fiir Anatomic, Physiologic, und wi&senschaftliche 

 Medicin, etc., 1847, p. 242. 2 From Kvpa, a wave. 



