CIRCULATION. 



87 



of the column is inverse to the 

 density of the manometric fluid. 

 For example, a given pressure will 

 sustain a far taller column of blood 

 than of mercury. 



The Mercurial Manometer. — 

 The method of Hales, in its orig- 

 inal simplicity, is valuable from 

 that very simplicity for demonstra- 

 tion, but not for research. The 

 clotting of the blood soon ends the 

 experiment, and, while it continues, 

 the tallness of the tube required for 

 the artery, and the height of the 

 column of blood, are very incon- 

 venient. It is essential to under- 

 stand next the principles of the 

 more exact instruments employed 

 in the modern laboratory. 



In 1828 the French physician 

 and physiologist J. L. M. Poiseuillc 

 devised means both of keeping the 

 blood from clotting in the tubes, 

 and of using as a measuring fluid 

 the heavy mercury instead of the 

 much lighter blood. He thereby 

 secured a long observation, a low 

 column, and a manageable man- 

 ometer. 1 The " mercurial man- 

 ometer" of to-day is that of Poi- 

 seuille, though modified (see Fig. 

 15). In an improved form it con- 

 sists of a glass tube open at both 

 ends, and bent upon itself to the 

 shape of the letter U. 'Phis is held 

 upright by an iron frame. If mer- 

 cury be poured into one branch of 

 the U, it will fill both branches to 

 an equal height. If fluid be driven 

 down upon the mercury in one 

 branch or "limb" of the tube, it 

 will drive some of the mercury out 

 of that limb into the other, ami the 

 rest at very unequal levels. The di 

 1 J. L. M. Poiseuille: Becherches 



Fig. 15. — Diagram of the recording mercurial man- 

 ometer and the kymograph; the mercury Is indicated in 

 deep black : M, the manometer, connected by the leaden 

 pipe, L, with a glass cannula tied into the proximal 

 stump of the left common carotid artery of a dog; A, 

 the aorta; C, the stop-cock, hy opening which the man- 

 ometer maybe made to communicate through RT, the 

 rubher tube, with ;i pressure bottle of solution of sodium 

 carbonate; F, the float of ivory and hard rubber; R, the 

 lighl Bteel rod, kept perpendicular bj B, the steel bear- 

 ing; /'. the glass capillary pen charged w ith quieklydry- 

 ing ink ; T, a thread which is caused, bj the weight of a 

 light ring of metal suspended from it, to press the pen 

 obliquely and gently agalnsl the paper with which la 

 covered /'. the brass " drum " of the kj mograph, « hicb 

 drum revolves in the direction of the arrow. The Bup 

 ports of the manometer and the body and clock-work 

 of the kymograph are omitted for the sake of simplicity. 

 The aorta and its brandies are draw n disproportionately 

 large for the sake of clearness. 



two surfaces of the mercury may come to 

 fference of level, expressed in millimeters, 

 sur la force du cceut aortique, Paris, 1828. 



