Copy 1, Volume 2

The study of medicine. Containing all the author's ... improvements / [John Mason Good].

  • John Mason Good
Date:
1829
Catalogue details

Licence: Public Domain Mark

Credit: The study of medicine. Containing all the author's ... improvements / [John Mason Good]. Source: Wellcome Collection.

    36/724 (page 26)
    I. Ma- chinery of the san- guineous system. by which the necessary supply of blood to parts is ren- dered secure, when any particular trunk is temporarily ob- structed by pressure, or permanently obliterated by this and other causes. After having divided, and ramified to a considerable ex- tent, and in a manner generally resembling the branching of a tree, the arteries, both of the greater and lesser. cir- culations, terminate in the general capillary system. The exact point at which the arteries end, and the capillaries begin, cannot be demonstrated. According to Bichat, it is where the blood ceases to be at all under the influence of the heart, and the circulation is first maintained alto- gether by a contractile power of the minute vessels, to which he allots the mysterious term of insensible organic contractility. But, this imaginary limit would not satisfy many physiologists, particularly those who argue, that the action of the heart always extends its effect to the capil- laries, as well as the arteries in general. Anatomists com- monly describe the arteries as terminating in excretory tubes, exhalants, veins, &c.; but, in reality, the capillary system constantly intervenes between those vessels and the regarded by some physiologists as merely mechanical tubes, the minute ones, or capillaries, are represented as the part of the vascular system, in which all the important objects of the circulation are mainly prepared and accom- plished, as nutrition, secretion, the oxydation of the blood, its decarbonization, &c. ] I have observed, that the force, with which the blood is at first projected from the heart, is progressively dimi- nished by the resistance it encounters in the thick and powerfully elastic tunic of the trunks or large arteries into which it is immediately propelled. There are two other causes which co-operate in producing a progressively di- minishing force. The first is the short angles against which the blood has to strike at the origin of all the dif- ferent branches; and the next, and most important, is the larger diameter of the general mass of the arteries, com- pared with that of the heart or the arteries from which they imimediately proceed; the range of the diameter augment- ing in proportion to the increase of the ramifications.