File:A text-book of physiology, for medical students and physicians (1907) (14775904434).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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meane of the mer-cury liulli the ga e can then l- forced out of .1 into a uiiaUe receiver loranal. 1 CHANGES IN AIR AND BLOOD IN RESPIRATION. 655 pressure in the alveoli of the lungs and circulates in the blood insmall amounts without exerting any immediate influence upon thetissues. Condition of Oxygen in the Blood.—That the oxygen is notheld in the blood merely in solution is indicated, in the first place,by the large quantity present and, in the second place, by the factthat this quantity does not vary directly with the pressure in thesurrounding medium. It is definitely known that by far the largestportion of the oxygen is held in chemical combination with thehemoglobin of the red corpuscles, while a much smaller portion,varying with the pressure, is held in solution in the plasma. Thecompound oxyhemoglobin possesses the important property thatwhen the pressure of oxygen in the surrounding medium falls suffi-ciently it begins to dissociate and free oxygen is given off. The proc-
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0 10 ^b 30 40 SO 60 70 80 90 100 110 110 130 140 150 160 Fig. 266.—Curves of dissociation of the oxyhemoglobin at different pressures ofoxygen. Five curves are shown to indicate that the dissociation of the oxyhemoglobinis greatly influenced by the presence of COo. The figures along the ordinates (10 to 100)indicate percentages of saturation of the hemoglobin with oxygen, while the figures alongthe abscissa (0 to 160) indicate different pressures of oxygen. The curve marked 5 mm.CO2 shows the amount of combination of oxygen and hemoglobin when the CO* is absentor present only in traces. In this curve at a pressure of 30 mms. of oxygen it will be seenthat the hemoglobin is 80 per cent, saturated with oxygen, while with a pressure of 40 mms.of COo, which approximates that in the body, the hemoglobin at the same pressure ofoxygen is only 50 per cent, saturated. (After Bohr.) ess of dissociation is facilitated also by increase of temperature,provided, of course, that it does not rise to

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