. Human physiology. vities; but the agency cannot begreat. It has recently been suggested by Liebig,^ that the fluids ofthe body, in consequence of the cutaneous and pulmonary transpira-tion, acquire a motion towards the skin and lungs; but it is not easyto see that this could have any important eftect on the circulation. There is another circumstance of a purely physical nature, whichmay exert some influence upon the flow of the blood along the veins;the expanded termination of the venas cavee in the right auricle. Toexplain this, it is necessary to premise a detail of a few hydraulic
. Human physiology. vities; but the agency cannot begreat. It has recently been suggested by Liebig,^ that the fluids ofthe body, in consequence of the cutaneous and pulmonary transpira-tion, acquire a motion towards the skin and lungs; but it is not easyto see that this could have any important eftect on the circulation. There is another circumstance of a purely physical nature, whichmay exert some influence upon the flow of the blood along the veins;the expanded termination of the venas cavee in the right auricle. Toexplain this, it is necessary to premise a detail of a few hydraulic an aperture A, Fig. 12-i, exist in a cistern X, the water will not issueat the aperture by a stream of uniform size; but, at a short distance Pliilosopliical Transactions for 1820, and An Inquiry into the Causes of Resjiiration,&c., 3d edit., Liverpool, 1833. 2 Researches on the Motion of the Juices in the Animal Body, by W. Gregory, M. D.,p. 74, London, 1848. FORCES THAT PROPEL THE BLOOD—VENA CONTRACTA, 431. from the reservoir, it will be contracted Fig. 124. as at B, constituting what has been termed the vena contracta. Now, it has been found, that if a tube technically called an adjutage be attached to this aperture, so as to accurately fit the stream, as at A B, Fig. 125, as much fluid will flow from the reservoir as if the aperture alone existed. Again, if the pipe B C be attached tothe adjutage A B, the expanded ex-tremity at A will occasion the flow ofwater from the reservoir to be greaterthan it would be if no such expanded extremity existed, in the ratio, accord- Vena Contracta. ing to Venturi, of 121 to 10; and if to the tube B C, a truncated conical tube C D be attached, the length ofwhich is nearly nine times the diameter of C; and the diameter of Cto that of D be as 1 to8; the flow of Fig. 125. water will be aug-mented in the pro-portion of 24 to12*1; so that, by thetwo adjutages A Band C D, the ex-penditure throughthe pipe B C is in-creased in the ratio of 24
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