File:A text-book of physiology (1893) (14597268488).jpg

Identifier: textbookofphysio18931fost (find matches)
Title: A text-book of physiology
Year: 1893 (1890s)
Authors: Foster, M. (Michael), Sir, 1836-1907 Lea, Arthur Sheridan. Chemical basis ..
Subjects: Physiology
Publisher: New York, London, Macmillan and Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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ricle, a second stroke drives more fluid intothe arteries, distending them this time more than it did before,and raising the mercury to a still higher level. A third, a fourth,and succeeding strokes produce the same effect, except that theadditional height to which the mercury is raised at each strokebecomes at each stroke less and less, until a state of things isreached in which the mercury, being on the fall when the stroketakes place, is by the stroke raised just as high as it was before, andthen beginning to fall again, is again raised just as high, and so on.With each succeeding stroke the arterial system has become moreand more distended; but the more^ distended it is the greater isthe elastic reaction brought into play. This greater elastic reactionmore and more overcomes the obstacle presented by the peripheral CiiAP. IV.) THE VASCULAK MECHANISM. 219 resistance, and drives the Huid more and more rapidly throughthe peripheral region. At last the arterial system is so distended,
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-^X Fig 33. Tracings taken from an artificial scheme with the peripheralresistance considerable. A, Arterial, V, Venous Manometer. and the force of the elastic reaction so great, that during the strokeand the succeeding interval just as much fluid passes through theperipheral region as enters the arteries at the stroke. In otherwords, the repeated strokes have established a mean arterial pres-sure which at the point where the manometer is affixed is raisedslightly at each ventricular stroke, and falls equally between thestrokes. Turning now to the venous manometer, Fig. 33 V, we ob-serve that each stroke of the pump produces on this much lesseffect than it did before the introduction of the increased peri-pheral resistance. The mercury, instead of distinctly rising andfalling at each stroke, now shews nothing more than very gentleundulations ; it feels to a very slight degree only the direct effectof the ventricular stroke; it is simply raised slightly above thebase line, and remains

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