ESTIMATION OF THE BLOOD-PRESSURE IN MAN. 165 



there is fixed a vertical rod attached to a series of levers, h, ?', k, e, one of which 

 writes its movements upon a surface moving at a uniform rate. The blood-pressure 

 and the periodic variations of the pulse are both recorded, although the latter ia 

 not done with absolute accuracy. 



Fig. 74. 



Blood-pressure curve of the carotid of a dog obtained with a mercurial manometer. 

 O - x = line of no pressure, zero line, or abscissa ; y - y' is the blood -pressure 

 tracing with small waves, each one caused by a heart-beat, and the large 

 waves due to the respiration. A millimetre scale shows the height of the 

 pressure in millimetres of mercury. 



[Hering improved Fick's instrument (Fig. 75). a, 6, c, is the hollow spring filled 

 with alcohol, and communicating at a with the lead tube, d, passing to the cannula 

 in the artery. To c is attached a series of light wooden levers with a writing- 

 style, s. The lower part of 4 dips into a vessel, e, filled with oil or glycerine which 

 serves to damp the vibrations of the levers. At / is a syringe communicating 

 with the tube, d, filled with solution of sodic carbonate, and used for regulating 

 the amount of fluid in the tube connecting the manometer with the blood-vessel. 

 The whole apparatus can be raised or lowered on the toothed rod, 7t, by means of 

 the millhead opposite, g, to which all the parts of the apparatus are attached.] 



(B.) In Man the blood-pressure may be estimated by means of a 

 properly graduated sphygmograph (p. 130). The pressure required to 

 abolish the movement of the lever indicates approximately the vascular 

 tension. Landois (Schobel) investigated the radial pulse in a healthy 

 student, and obtained a mean blood-pressure equal to 550 grammes. 



(2.) By a manometric method v. Basch estimated the blood-pres- 



