Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee.

  • Gamgee Arthur, 1841-1909.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Elements of human physiology / by L. Hermann ; translated from the sixth edition by Arthur Gamgee. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

    99/620 (page 79)
    [Ooagulation is retarded by cold, and is indeed indsEnitely postponed if tliis Tje sufficient to freeze the blood. Blood which has been frozen before coagula- tion has occiu-red may be rapidly thawed and frozen again without coagulation talcing place (Hewson We cannot yet decide whether the non-coagulation is due to the non-formation of fibrin-ferment or merely to the fact tbat one of the conditions for the union of the fibrin generators, even in the presence of fibrin-ferment, is a temperature above freezing point. Ooagulation may be prevented by the addition of sufficient quantities of neutral salts to blood, such as sodiiun sulphate and potassium nitrate. Thus Hewson found that when six ounces of blood are mLxed with half-an-ounce of the former salt reduced to powder, the blood does not coagulate on being ex- posed to the air; but when to the mixtiu-e twice the quantity of water is added, in a short time the whole becomes converted into a jelly, owing to the formation of fibrin. Ooagulation may be also checked by precipitating the fibriuoplastic sub- stance by means of carbonic acid or other weak acids ; in this case, one of the fibrin generators having been removed, coagulation can necessarily not occui, unless it be restored.] II. THE CIECULATION OF THE BLOOD. The blood circulates continually, and with great speed, through- out all parts of the body, in the paths prescribed for it by the vascular system, which, under normal circumstances, it never leaves. All the matters given up by the blood have, therefore, to pass through the closed vascular wall, and with few exceptions (passage of lymph into the blood), this is the case with matters absorbed into the blood. Only the thinnest portions of the vas- cular system, viz. the capillaries, permit of this exchange taking place. Seeing that the vascular system is completely closed, and that the movement of the blood is always in the same direction, it is clear that that movement must be of the natm-e of a circu- lation. The vascular system may therefore be pictured as a system of continuous closed tubes, with many branches ; the finest ramifica- tions of this system correspond to the capillaries. Only in two places is the system perfectly simple ; these are the aorta and the pulmonary artery, each with its appended half of the heart. From each of these places the blood can only ]-each the other through a capillary system: there are, therefore, two principal capillary systems, through both of which every particle of blood must pass once at each circulation—the pulmonic capillary system, and the systemic capillary system. The functional difference between these capil- lary systems depends on the character of the changes which the blood which they contain undergoes (see Chapter V.): in the pul- monic capillaries the blood takes up oxygen, and gives off carbonic acid ; the reverse takes place in the systemic capillaries. Through- out the whole of the passage, therefore, from the pulmonic ' Hewson, The Works of, printed by the Sydenham Society, 1846, p. 17,