An introduction to medical literature, including a system of practical nosology : intended as a guide to students, and an assistant to practitioners. Together with detached essays, on the study of physic, on classification, on chemical affinities, on animal chemistry, on the blood, on the medical effects of climates, on the circulation, and on palpitation / by Thomas Young.

Date:: 1823

Credit: An introduction to medical literature, including a system of practical nosology : intended as a guide to students, and an assistant to practitioners. Together with detached essays, on the study of physic, on classification, on chemical affinities, on animal chemistry, on the blood, on the medical effects of climates, on the circulation, and on palpitation / by Thomas Young. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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tinued by anastomosis, after the arteries had been tied above the swellings. Medicoch. tr. X. 233.” Med. Lit. Ed. 1. p. 104.] These are the principal circumstances which require to be considered, with respect to the simple transmission of the blood through the arteries into the veins, without regard to the alternate motions of the heart, and to the elastic and muscular powers of the vessels. I shall next examine the nature and velocity of the propagation of the pulse. The successive transmission of the pulsations of the heart, through the length of the arteries, is so analogous to the motion of the waves on the surface of water, or to that of a sound trans- mitted through the air, that the same calculations will serve for determining the principal affections of all these hinds of motion ; and if the water, which is agitated by waves, is sup- posed to flow at the same time in a continued stream, and the air which conveys a sound to be carried forwards also in the form of a wind, the similitude will be still stronger. The coats of the arteries may perhaps be considered, with- out much inaccuracy, as perfectly elastic, that is, as pro- ducing a force proportional to the degree in which they are extended beyond their natural dimensions; but it is not im- possible that there may be some bodies in nature, which differ materially from this general law, especially where the distension becomes considerable : thus there may be sub- stances which exhibit a force of tension proportional to the excess of the square, or the cube of their length, beyond a certain given quantity. It is safest therefore to reason upon the elasticity of any substance, from experiments made with- out any great deviation from the circumstances to which the calculation is to be applied. For this purpose, we may again employ some of the many excellent experiments contained in Hales’s hajmastatics. It appears, that when any small alteration was made in the quantity of blood contained in the arteries of an animal, the height of the column, which measured the pressure, was al-

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