A text-book of physiology (1893) (14597248349)

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

Text Appearing Before Image:

of the movements of the column of mercury in the mano-meter may be taken either on a smoked surface of a revolving cylinder(Fig. 2), or by means of ink on a continuous roll of paper, as in themore complex kymograph (Fig. 29). § 116. By the help of the manometer applied to variousarteries and veins we learn the following facts: (1) The mean blood pressure is high in all the arteries, butis greater in the larger arteries nearer the heart than in thesmaller arteries farther from the heart; it diminishes, in fact,along the arterial tract from the heart towards the capillaries. (2) The mean blood pressure is low in the veins, but is greaterin the smaller veins nearer the capillaries than in the larger veinsnearer the heart, diminishing, in fact, from the capillaries towardsthe heart. In the large veins near the heart it may be negative, 14 210 BLOOD PEESSUEE. (Book i. that is to say, the pressure of blood in the vein bearing on theproximal descending limb of the manometer may be less than

Text Appearing After Image:

Fig. 29. Ludwigs Kymograph for recording on a continuous roll of paper. the pressure of the atmosphere on the ascending distal limb, sothat when communication is made between the interior of the veinand the manometer, the mercury sinks in the distal and rises inthe proximal limb, being sucked up towards the vein. The manometer cannot well be applied to the capillaries, but wemay measure the blood pressure in the capillaries in an indirect way.It is well known that when any portion of the skin is pressed upon,it becomes pale and bloodless ; this is due to the pressure drivingthe blood out of the capillaries and minute vessels, and preventingany fresh blood entering into them. By carefully investigatingthe amount of pressure necessary to prevent the blood enteringthe capillaries and minute arteries of the web of the frogs foot, orof the skin beneath the nail or elsewhere in man, the internalpressure which the blood is exercising on the walls of the capil-laries and minute arteries and v

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1893

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