Volume 2

The anatomy and physiology of the human body.

  • Bell, John, 1763-1820.
Date:
1826
Catalogue details

Licence: Public Domain Mark

Credit: The anatomy and physiology of the human body. Source: Wellcome Collection.

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

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    the gills, divide into exquisitely small brandies pro- ducing that feathery appearance which is so beautiful. Those minute subdivisions* of the bronchial vessels expose the blood to tlie air. This may explain to us how in the human lungs the exposing of the blood, even with the interposition of membranes and of the arterial coats, may be sufficient for the oxy- dation of the blood. All the blood thus oxygenated is returned by veins, corresponding exactly in number and arrangement with their arteries : and the heart being turned aside, and all the other viscera taken out, the veins are seen accompanying their arteries and emerging from the gills to form the aorta. Thirdly, The aorta is formed by the veins of the gills, and the veins of the gills lie close upon the skull of the fish, and the aorta upon the back-bone; and this vessel is in one sense a vein, since it is a continuation of those veins which return the blood of the gills; but both in office and form it is a true aorta; in office, because it distributes blood to the whole body ; and in form, because it no sooner swells out into the shape of an aorta than its coats grow hard, strong, muscular, fit for its office, while those of the veins from which it is formed are pellucid, delicate, and very tender. The aorta is full of the oxydated blood of the gills ; and although, by the delicate circulation of the gills, it has lost all commu- nication with the heart, it circulates this oxydated blood through the body to all the muscles, glands, viscera, &c. without the intervention of a new heart. The veins which return the blood of this aorta are the ordinary veins; they arrive in two great branches at the heart, and need not be further explained. I will not be at the trouble to repeat the tedious calculations of authors concerning the immense sur- face which the gills expose: let the student look to the gills, and he will presently, with the help of this short sketch, understand how the whole function goes on.