A text-book of human physiology : designed for the use of practitioners and students of medicine / by Austin Flint.

  • Flint, Austin, 1836-1915.
Date:
1876
Catalogue details

Licence: Public Domain Mark

Credit: A text-book of human physiology : designed for the use of practitioners and students of medicine / by Austin Flint. Source: Wellcome Collection.

Provider: This material has been provided by The University of Leeds Library. The original may be consulted at The University of Leeds Library.

    106/1010 (page 84)
    serous membranes, tendons, etc. In none of the tissues do we find capillaries penetrat- ing the anatomical elements, as the ultimate muscular or nervous fibres. Some tissues receive no blood, at least they contain no vessels which are capable of carrying red blood, and are nourished by imbibition of the nutrient plasma of the circulating fluid. Examples of these, which are called extra-vascular tissues, are cartilage, nails, and hair. The foregoing anatotnical sketch gives an idea of how near the blood is brought to the tissues in the capillary system, and how, once conveyed there .by the arteries, and the supply regulated by the action of the muscular coat of the smaller vessels, the blood is distributed for the purposes of nutrition, secretion, absorption, exhalation, or whatever function the part has to perform. This will bo still more apparent when we come to consider the course of the blood in the capillaries and the immense capacity of this sys- tem, as compared with the arteries or veins. The capacity of the capillary system is immense. It is only necessary to consider the great vascularity of the skin, mucous membranes, or muscles, to realize this fact. In injections of these parts, it seems, on microscopical examination, as though they con- tained nothing but capillaries. In preparations of this kind, the elastic and yielding coats of the capillaries are distended to their utmost limit. Under some circumstances, in health, they are largely distended with blood, as the mucous lining of the alimentary canal during digestion, the whole surface presenting a vivid-red color, indicating the great richness of the capillary plexus. Various estimates of the capacity of the capil- lary, as compared with the arterial system, have been made, but they are simply approxi- mative, and there seems to he no means by which an estimate, with any pretensions to accuracy, can be formed. The various estimates which are given are founded upon cal- culations from microscopical examinations of the rapidity of the capillary circulation as compared with the circulation in the arteries. In this way, it has been estimated tlmt the entire capacity of the capillary system is from five hundred to eight hundred times that of the arterial system. It must be evident to any one who has witnessed the capU- lary circulation under tlie microscope, that the conditions under which the animal under exammation is placed are liable to interfere with the current of blood; and the periodi- cal congestion of certain parts, the fugitive flushes of the skin, the condition of the smallest arteries induced by changes of temperature, exercise, etc., make it evident that the current of blood is liable to great variations. It is impossible to strictly apply to the capillary circulation in the various parts of the human subject observations on the wing of a bat or the mesentery of a cat. We must consider, then, these estimates as mere suppositions, and they are given for what they are worth. Phenomena of the Capillary Circulation.—The most convenient situation for the practical study of the capillary circulation is the tongue or the web of the frog. Here may be studied, not only the movement of the blood in the true capillaries but the cir- culation in the smallest arteries and veins, the variations in cahber of these vessels, especially the arterioles, by the action of their muscular tunic, and, indeed, the_ action of vessels of considerable size. This has been a most valuable means of studying the circulation in the capillaries as contrasted with the flow in the smaU arteries and veins, and the only one, indeed, which could give us any definite idea of the action of these vessels. The magnificent spectacle of the capillary circulation was first observed by Malpighi, in the lungs, and afterward by Leeuwenhoek, Spallanzani, Hauler, Cowper, others, in other parts. We see the great arterial rivers, in which the blood flows with wonde - ful rapidity, branching and subdividing, until the circulating fluid is l^i;ojight to the net- work of fine capillaries, where the corpuscles dart along one by one. The blood is then collected by the veins and carried in great currents to the heart. This ^^^l^l^'t'o;' the student of Nature, is of inexpressible grandeur; and our admiration is not dimin- ished when we come to study the phenomena in detail. We find here a subject as inter-