BLOOD, a well known fluid, which circulates through the arteries, veins, &c. of animal-bodies, and nourishes all their parts.
Blood is composed of a thin watery liquor called serum, and a thick red part called coagulum, which, when viewed by the microscope, appears to consist of red globules of a certain determined magnitude. These globules are generally believed to be of the same magnitude in all animals that have red blood.
As blood is originally derived from our aliment, it must consist of the same principles, and consequently abound with salts and oils. The salts of the blood are partly of the fixed neutral kind, and partly such as are rendered semi-volatile by the heat and motion to which they are subjected: Both irritate the sensible nervous parts of animals; for it is well-known that any kind of salt applied to the eye gives great uneasiness. From these qualities of blood the late learned and celebrated Dr Whytt concluded that it must be well fitted to communicate a gentle stimulus to those sensible nerves which terminate on the internal surface of the auricles and ventricles of the heart; and consequently that the contraction of the heart is principally owing to this cause. The diameter of a red globule is computed to be about part of an inch. See CIRCULATION; and for the analysis of blood, see CHEMISTRY.
Authors are not agreed in regard to the quantity of blood contained in the human body; some making it only 10 pounds, whilst others make it to be 20, 60, or even 100 pounds: But then these last comprehend the juices of the lymphatic vessels under the term blood. As to the quantity of current blood in a horse, the ingenious Dr Hales found it be, at a low computation, 1105 cubic inches, or 42.2 pounds.