ESTIMATION OF THE BLOOD-PRESSURE. 



119 



about 7000 litres of blood must pass through the Jungs in 24 hours. If one calculates 100,000 

 heart-beats in 24 hours, then at each systole only 70 cubic centimetres are discharged. 



Fig. 100. 

 I. Scheme of C. Ludwig's kymograph. II. Fick's spring-kymograph. 



84. ESTIMATION OF THE BLOOD-PRESSURE. (A) In Animals : (1) Methods of Hales. 

 The Rev. Stephen Hales (1727) was 

 the first to introduce a long glass tube 

 into a blood-vessel in order to estimate 

 the blood-pressure by measuring the 

 height of the column of blood. 



The tube was provided at its lower 

 end with a copper tube bent at a right 

 angle (Pitot's tube). [The tube he used 

 was one-sixth of an inch bore and about 

 9 feet long, and was inserted into the 

 femoral artery of a horse. The height 

 to which the blood rose in the tube 

 was noted, as well as the oscillations 

 that occurred with every pulsation. 

 From the height of the column of fluid 

 he calculated the force of the heart. ] 



(2) The Hsemadynamometer of Poi- 

 seuille (1828). This observer used a 

 U-shaped tube partially filled with 

 mercury a manometer which was 

 brought into connection with a blood- 

 vessel by means of a rigid tube. [The 

 mercury oscillated with every pulsa- 

 tion, and the extent of the oscillations 

 was read off by means of a scale attached 

 to the bent tube. He called the instru- 

 ment a hoeniadyinamomcter. ] 



[(3) Vierordt used a tube 5 or 6 feet 

 long, and filled it with a solution of 

 sodium carbonate, thus preventing 

 much blood from entering the tube, 

 while at the same time the soda solu- 

 tion prevented the coagulation of the 

 blood.] 



(4) C. Ludwig's Kymograph. 



C. Ludwig employed a U-shaped 



manometer, but he placed a light float (fig. 100, d, s) upon the surface of the mer 



Fig. 101. 

 Ludwig's improved revolving cylinder, R, moved by the 

 clock-work in the box A, and regulated by a Foucault's 

 regulator placed *on the top of the box. The disc, D, 

 moved by the clock-work, presses upon the wheel, n, 

 which can be raised or lowered by the screw, L, thus 

 altering the position of n on D, so as to cause the cylin- 

 der to rotate 'at different rates. The cylinder itself can 

 be raised by the handle, U. On the left side of the 

 figure is a mercurial manometer. When the cylinder 

 is used, it is covered with smoked smooth paper. 



