METHODS OF MEASURING ARTERIAL BLOOD-PRESSURE 221 



The essential part of a recording kymograph consists of a uniformly 

 revolving cylinder accurately centered and carrying a paper on which a record 

 is made of the physiological change which is being studied. This cylinder 

 or drum may be driven by a weight, clock spring, electric motor, or other 

 mechanical device that insures uniformity of speed and which is capable of 

 speed regulation. The cylinder is covered with glazed paper, blackened in 

 the flame of a lamp, and the mercury manometer is so supported that its 

 float, provided with a style, writes on the cylinder as it revolves. In some 

 of the instruments, especially Ludwig's continuous paper kymograph, a 

 long paper band is made to pass over the recording surface and the record 

 itself is written by various devices carrying ink. 



There are also many ways in which the mercury manometer may be 

 varied; in figure 185 is seen a form which is known as Ludwig's. In order 

 to obviate the necessity of a large quantity of blood entering the tube of the 

 apparatus and being lost to the animal, it is usual to have some arrangement 

 by means of which the mercury may, previous to the experiment, be forced 



wo 

 to 



FIG. 186. Tracing of Normal Arterial Pressure in the Dog, Obtained with the 

 Mercurial Manometer. The smaller undulations correspond with the heart-beats; the 

 larger curves with the respiratory movements. Pressure is in millimeters of mercury as 

 shown by the scale to the left. Time in seconds. 



up in the tube of the manometer to the pressure level corresponding to 

 approximately the mean pressure of the artery experimented with, so that the 

 writing style simply records the variations of the blood-pressure above and 

 below the mean pressure. This is done by causing the anti-coagulant 

 solution, generally a saturated solution of sodium carbonate or of 10 per 



