Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/138

114]  in Paris, were both instituted after civil wars, which had animated the people, and excited their activity and emulation.

maintained, that men were indebted for the acquisition of their arts to brutes; that the spider taught them '; the swallow, '; the nightingale, , and so forth.

There are various particular arts, as those of, , , &c. of which we propose to treat in their respective places.  Artemisia absinthium, L. See.  ARTERY, or a pulsating blood-vessel, is a cylindrical canal, conveying the blood immediately from the heart to all the parts of the body. On examining the structure of the largest of these vessels, such as the aorta, and the pulmonary artery, it may be distinctly seen, that each is composed of three coats; namely, 1. The external coat, which is of a cellular texture, loose on the outside, but growing progressively firmer towards the inner part; 2. A fibrous spiral, or rather circular membrane, of a yellowish colour, and of which there are several strata, according to the size of the artery; 3. The innermost coat, or a thin, extremely smooth and transparent membrane, keeping the blood in its canal, which otherwise, upon the dilatation of an artery, would easily separate the spiral fibres from each other.

From the trunk of every artery there arise branches; from these again extend ramifications of blood-vessels, which become progressively smaller, so that their distribution may be traced by the microscope, in more than twenty different divisions, nay, to an almost infinite number. The arteries, however, do not, as has been erroneously asserted by several anatomical writers, become narrower, and assume a conic form in their continued progress; on the contrary, they seem uniformly to remain cylindrical, insomuch that, in their ramifications, a smaller cylinder always arises from a larger one, and where the former proceeds from the latter, it generally presents a slight swelling at this vascular joint, if this expression be admissible. The aggregate diameter of all the branches of one trunk is somewhat larger than that of the trunk itself; an observation which also applies to the veins.

On account of their thicker membranes, the arteries possess a greater degree of elasticity than the veins; though the latter are more capable of resisting the mechanical force of the blood, and are less liable to rupture. It farther deserves to be remarked, that, with the increase of years, the coats of the arteries acquire firmness, while those of the veins become weaker. This, in some measure, accounts for the circumstance that persons, between the age of eighteen and thirty-five, are more liable to phthisical and other complaints, which depend chiefly on an increased action of the arterial system; because, after that period, the arteries already possess sufficient vigour and firmness, to overcome the additional impetus of the circulation. Hence, too, we may comprehend why sthenic or inflammatory diseases seldom occur at certain stages of life, when the whole system possesses that degree of re-action, which is necessary to maintain a due equilibrium  tween