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HAND-BOOK OF PHYSIOLOGY. 



blood-pressure balances; the weight of the soda solution being sub- 

 tracted. 



For the estimation of the arterial tension at any given moment, no 

 further apparatus than this, which is called Poiseuille's hcemadynamometer, 

 is necessary; but for noting the variations of pressure in the arterial sys- 

 tem, as well as its absolute amount, the instrument is usually combined 



with a registering apparatus and in this form is 

 called a kymograph. 



The kymograph, invented by Ludwig, is 

 composed of a hasmadynamometer, the open 

 mercurial column of which supports a floating 

 piston and vertical rod, with short horizontal 

 pen (Fig. 134). The pen is adjusted in con- 

 tact with a sheet of paper, which is caused to 

 move at a uniform rate by clockwork; and 

 thus the up-and-down movements of the mer- 

 curial column, which are communicated to the 

 rod and pen, are marked or registered on the 

 moving paper, as in the registering apparatus 

 of the sphygmograph, and minute variations 

 are graphically recorded (Fig. 135). 



For some purposes the spring kymograph of 

 Fick (Fig. 136) is preferable to the mercurial 

 kymograph. It consists of a hollow C-shaped 

 spring, filled with fluid, the interior of which 

 is brought into connection with the interior 

 of an artery, by means of a flexible metallic tube and cannula. In 

 response to the pressure transmitted to its interior, the spring, c, tends 

 to straighten itself, and the movement thus produced is communicated 

 by means of a lever, Z>, to a writing-needle and registering apparatus. 



FIG. 134. Diagram of mercu- 

 rial manometer, a. Floatiag rod 

 and pen. b. Tube, which commu- 

 nicates with a bottle containing 

 an alkaline solution, c'. Elastic 

 tube and cannula, the latter being 

 intended for insertion in an artery. 



FIG. 135. Normal tracing of arterial pressure in the rabbit obtained with the mercurial kymo- 

 graph. The smaller undulations correspond with the heart beats; the larger curves with the respir- 

 atory movements. (Burdon-Sanderson.) 



Fig. 137 exhibits an ordinary arterial pulse-tracing, as obtained by the 

 spring-kymograph . 



From observations which have been made by means of the mercurial 

 manometer, it has been found that the pressure of blood in the carotid of 

 a rabbit is capable of supporting a column of 2 to 3^ inches (50 to 90 



