Blood Pressure. Usually refers to pressure of blood in main arteries, which in ‘normal’ human beings fluctuates roughly between 10 and 80 mm. of mercury according to stage of heart beat (maximum at systole, minimum at diastole). Pressures throughout the whole circulation diminish from arteries next to heart round to veins next to heart; in mammals reaching atmospheric or less in large veins.

.Blood Serum. Fluid expressed from clotted blood or from clotted blood plasma. Roughly, plasma deprived of fibrin, but containing products of clotting mechanism.

Blood Sugar. Glucose (25%) dissolved in blood. In vertebrates supplied to blood by liver (where it is stored as glycogen) and removed there from by all body cells for use as food. In mammals maintained at a fairly constant level (80-180 mg per 100 cc blood in man), chiefly controlled  by hormones (insulin and glucagon from pancreas, adrenaline and glucocorticoids from adrenal gland). If level is too low (hypoglycaemia) the cells are starved, and this rapidly damages brain-cells; if too high (hyperglycaemia as in diabetes mellitus) glucose is excreted by kidney.

Bog. An area of peat formation, typically in upland situations, which supports an extremely oligatrophic vegetation.

Bolus. A soft mass of chewed food, suitable for swallowing, shaped by the tongue in the Buccal cavity.

Bone. Skeletal substance peculiar to vertebrates. Consists of cells distributed in a matrix consisting largely of collagen fibres together with a complex salt (bone salt) mainly of calcium and phosphate. Bone salt 60 per cent by weight of bone, is responsible for hardness; collagen for tensile strength. The cells are connected  y fine channels which permeate the matrix. Large channels contain  blood vessels and verves. Some bones, e.g. long bones and ribs of mammals, contain narrow, a tissue which form white blood cells.

Bone marrow. A modified connective tissue of a vascular nature found in long bones and some flat bones of vertebrates.

Bony Fish. Osteichthyes.