On slight ailments : and on treating disease / by Lionel S. Beale.
- Lionel Smith Beale
- Date:
- MDCCCXC [1890]
Licence: Public Domain Mark
Credit: On slight ailments : and on treating disease / by Lionel S. Beale. Source: Wellcome Collection.
Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.
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![:allowed to return, it fills these vessels and distends them to precisely the same degree as before. By this simple experiment we conclusively prove not only that the capillary vessels are dilated, but dilated to a definite extent, so that ■every capillary will resume the same diameter, and is capable of retaining this, at any rate, for some hours, though the blood may be thoroughly squeezed out and allowed to run back as often as you please, ilow is this brought about ? By what mechanism is it effected, and how can the phenomenon be accounted for ? The change is complex, and not to be explained in a few words, but as it illustrates some very important physiological and pathological principles, the matter is well worthy of attentive consideration. In the first place, we must take note of the conditions which determine and regulate the flow of blood at a certain rate through the capillary vessels, and these are somewhat complex. The capillaries are elastic tubes which have no power, as far as is Tnown, of active contraction. They can be distended, and they will recoil or contract, so as to be very much less than their ordinary diameter, indeed they may be so reduced as to appear like mere lines, their cavity being for the time obliterated, not a blood-corpuscle passing through them. Nevertheless, the capillary has no active power of contraction or dilatation. Its thin walls are eminently elastic, and yield if blood or other fluid is forced into the tube by pressure. If they are allowed to react upon the fluid it will be gradually expelled, and the cavity of the tube almost obliterated, the capillary vessel looking like a fine cylindrical cord. If the little arteries are distended and enlarged, more blood will be permitted to pass into the capillaries,, and these tubes will be distended, and their walls stretched. If the diameter of the arteries becomes reduced, the capillaries will shrink. These pheno- mena are repeated whenever the pressure by which the blood is forced into the vessels is increased or reduced. The Degree of Contraction of the Minute Arteries determined and maintained by Nerve Action.—The smaller arteries, we know, are capable of undergoing very great alterations in calibre, the alterations being of an active character. By active I mean that the diameter of a small artery can be maintained for a time at a certain uniform standard, the canal being completely obliterated, or increased to twice the area of its usual section, or half the area, as the case may be—and this irrespective of any temporary changes produced by mechanical pressure applied from time to time. The smaller arteries are encircled by numerous muscular fibres, ]-)laced as close as possible to one another, often arranged in very many layers. This muscular tissue constitutes the greater part of the thick- ness of the arterial walls. An idea may be formed of the arrangement](https://iiif.wellcomecollection.org/image/b2130340x_0318.jp2/full/800%2C/0/default.jpg)
