162 ESTIMATION OF THE BLOOD-PRESSURE. 



through the systemic circulation, it follows that the right ventricle must 

 be just as capacious as the left. The capacity of the ventricles has 

 been estimated in the following ways : 



(1.) Directly, by filling the dead ventricle with blood (Santorini, 1724; Legallois 

 and Collin). This method is unsatisfactory and inaccurate. (2.) All the vessels of 

 the relaxed heart are ligatured, the heart excised, and the contents of the cavities 

 estimated (Abegg, 1848). (3.) Volkmann estimated the capacity to be ^ of the 

 body- weight i.e., for a man of 75 kilos. =187*5 grms. 



84. Estimation of the Blood-Pressure. 



(A.) In Animals : Method 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, i.e., how high the 

 blood rose in the tube. 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 nine 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 Poiseuille, This observer (1828) 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 pulsation, and the extent of the oscillations was read off by means of a 

 scale attached to the bent tube. He called the instrument a hcemadynamometer}. 



[(3.) VierOfdt used a tube five or six 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 solution prevented the coagulation of the blood.] 



(4.) C. Ludwig's Kymograph. C. Ludwig employed a U-shaped mano- 

 meter of the same kind, but he placed a light float (Fig. 72, d, s) upon 

 the surface of the mercury in the open limb of the tube. A 

 writing-style, /, placed transversely on the free-end of the float, 

 inscribed the movements of the float and, therefore, of the mercury 

 upon a cylinder, c, caused to revolve at a uniform rate. This 

 apparatus registered the height of the blood-pressure, as well as 

 the pulsatile and other oscillations occurring in the mercury. Volk- 

 mann called this instrument a kymograph or " wave-writer." The 

 difference of the height of the column of mercury, c, d, in both limbs 

 of the tube indicates the pressure within the vessel. If the height of 

 the column of mercury be multiplied by 13*5, this gives the height 

 of the corresponding column of blood. Setschenow placed a stop-cock 

 in the lower bend, h, of the tube. If this be closed so as just to 

 permit a small aperture of communication to remain, the pulsatile 

 vibrations no longer appear, and the apparatus indicates the mean 

 pressure. By the term mean pressure is meant the limit of pressure, 

 above and below which the oscillations occurring in an ordinary blood- 



