CIRCULATION. 



379 



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- 

 tioD, 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. Poiseuille 

 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- 



omprpr" nf to Hav i^ that of Poi FIG. lOO.-Diagram of the recording mercurial man- 



" ometer and the kymograph ; the mercury is indicated in 



Seuille, though modified (see Fig. deep black : J/, the manometer, connected by the leaden 



-i f\r\\ T i ^ -j. pipe, L, with a glass cannula tied into the proximal 



)0> In an improved form it con- s p tump of the left common carotid artery of a dog . A% 



Sists of a glass tube Open at both the aorta; C, the, stop-cock, by opening which the man- 

 , , . ._ , ometer maybe made to communicate through RT, the 

 ends, and bent Upon itsell tO the rubber tube, with a pressure-bottle of solution of sodium 

 Shape Of the letter U. This is held carbonate ; F, the float of ivory and hard rubber; R, the 

 * . light steel rod, kept perpendicular by B, the steel bear- 

 Upright by an iron frame. If mer- ing; P, the glass capillary pen charged with quickly dry- 

 on rv hp nonrprl into nnp branch of ing ink ; T > a thread wbich is caused ' b y the wei ^ ht of ft 



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



the U, it will fill both branches to obliquely and gently against the paper with which is 

 11 i .L TI J3 i t, J covered D, the brass " drum " of the kymograph, which 



an equal height. It fluid be driven drum revolves in the dire etion of the arrow. The sup- 

 down Upon the mercury in One P rts of the manometer and the body and clock-work 

 , . , of the kymograph are omitted for the sake of simplicity. 

 branch or "limb Ot the tube, it The aorta and its bran ches are drawn disproportionately 



will drive some of the mercury out lar s e for the sake of clearness, 

 of that limb into the other, and the two surfaces of the mercury may come to 

 rest at very unequal levels. The difference of level, expressed in millimeters, 

 1 J. L. M. Poiseuille: Recherches sur la force du cceur aortique, Paris, 1828. 



