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- 

 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. 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- 



rnnprpr" of to dflv iq 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 : M, the manometer, connected by the leaden 

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



100). In an improved form it con- ^ tumpof the left common carotid artery of a dog ; A, 



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



, . . , , ometer may be made to communicate through RT, the 



ends, and bent Upon itselt to the rub ber 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 



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



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



CUry be poured into One branch of to*'' ^, a thread which is caused, by the weight of a 



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 



an equal height. If fluid be driven 



down Upon the mercury in one P or ts of the manometer and the body and clock-work 



K V. T K " f 4-V. t- k of the kymograph are omitted for the sake of simplicity. 



limb OI the tube, it The aorta and its branches are drawn disproportionately 



will drive some of the mercury out lar * 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: Eecherches sur la force du cceur aortique, Paris, 1828. 



