File:A text-book of physiology, for medical students and physicians (1907) (14777777082).jpg

Identifier: textbookofphysio1907howe (find matches)
Title: A text-book of physiology, for medical students and physicians
Year: 1907 (1900s)
Authors: Howell, William H. (William Henry), 1860-1945
Subjects: Physiology Physiology
Publisher: Philadelphia, London, W.B. Saunders Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

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AB: An, or ab = According to this method,Vierordt calculated that thevelocity of the blood in thehuman capillaries is equal toabout 0.6 to 0.9 mm. persecond. In the arteries, more- , , . Fig. 185.—Diagram of the eve to show the con- OVer, It may be Observed struction used to determine the size of the retinal 4-V.^i- 4-U„ _ _ i j. image when the size of the external object is known: that the average Velocity n, The nodal point of the eye. See text. diminishes the farther one goes from the heart,—that is, the smaller the artery,—andreaches its minimum when the arteries pass into the capillaries.Thus, Volkmann reports for the horse the following figures: Ca-rotid, 300 mms.; maxillary, 232; metatarsal, 56 rams. In the veinsalso the same fact holds. The smaller the vein—that is, the nearerit is to the capillary region—the smaller is its velocity, the maxi-
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lig. 186.—Schematic representation of the relative velocities of the blood-current in >.i lie .1 « mI m . v torn: «, The arterial side, indicating the changes with each heart beat and the fall of mean velocity as the arterial bed widens; c, the capillary ill- gieat diminution in veloeit y em re, pond- with the groat widening of the bed;r, the : Showing the gradual increase Inward the heart, and represented as entirelj uniform, although, as a matter of fact, the velocity in the large veins is affected bythe respirations and to a small extent by the heart beat, owing t the phenomenon knownas the venous pulse p. 513). mum velocity being found in the vena cava. The general rela-tions of the velocity of the blood in the arteries, capillaries, andveins may be expressed, therefore, by a curve such as is shownin Fig. iso. * Archiv I, physiologische Heilkunde, 15, 2~>.r>, ix.r>(j. VELOCITY AND PRESSURE OF BLOOD-FLOW. 471 Explanation of the Variations in Velocity.—The

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