Page:Willich, A. F. M. - The Domestic Encyclopædia (Vol. 1, 1802).djvu/320

290] from the application of mustard-seed, or horse-radish.  BLITE, the small red, or Amaranthus blitum, L. is an indigenous species of the amaranth, which is frequently found growing on rubbish, &c. It flowers in July and August: on the Continent its seed is used as a substitute for millet, and the leaves are dressed and eaten like spinach.  Blite, the upright. See round-leaved.  BLOOD, the most copious fluid in the animal body, and essentially necessary to the preservation of life: it is generally of a red, but in most insects, and in all worms, of a white colour.

The human body is, by Dr., supposed to contain at least one half of its weight in blood; including in this computation all that exists in the lymphatic ducts, nerves, or any other vessel. This computation, however, is exaggerated; and we believe that the greatest quantity in a full-grown adult, seldom exceeds thirty pounds weight. Its most remarkable property is that of incessantly circulating in the cavities of the heart, arteries, and veins, while the animal is alive. Although appears to have possessed a faint idea of this admirable process, when he says, "that all the blood vessels spring from one; and that this one has neither beginning nor end; for where there is a circle, mere can be no beginning;" yet as he was not acquainted with the office of the valves, he could neither comprehend, nor demonstrate, the circulation of the blood. This most important of all discoveries in physiology, was resolved for the immortal, who first ascertained the true nature and uses of the valves, and about the year 1616, taught, in his Lectures at Cambridge, that justly admired doctrine, the substance of which he published in 1628. He proved that, in most animals, the blood circulates in arteries and veins, and through the medium of one, two, or more hearts (see ); that in arteries it moves from the trunk to the branches; and that, meeting there with the branches of veins, it returns in a languid state to the heart; that the heart communicates a new impulse, and propels it to the trunk of the arteries; and that by these, the thickness of their coats, exerting muscular force, again drive it into the veins.—Valves are situated in every part of this circulating course, in order to prevent the return of the blood.

The colour of this fluid in the arteries is of a florid hue; but somewhat darker in the veins, except in those of the lungs, in which it is of a lighter cast. When exposed to the open air, the blood gradually separates into two parts, namely, the serum, or a yellowish, sometimes greenish fluid, and the crassamentum, or cake, which resembles a red mass swimming distinctly on the top. The latter contracts greatly in its dimensions, and increases in solidity; properties which depend on the state of the individual at the time when the blood is drawn. Hence, in vigorous persons, when attacked with an inflammatory disease, the solid part is so tough that it resembles a piece of flesh, and has therefore been called the buffy coat; whereas, in other diseases, it is very soft and tender, breaking in pieces on the slightest touch. By chemical analysis, it discovers the same principles with other animal substances; yield-