SECRETARY BIRD

(Serpentarius sag it tar i us), sO named on account of the pen-like tuft of feathers stuck clerk wise at the back of the head; crane-like African birds which feed on insects and reptiles. SECRETION. A substance formed or separated from the blood by various glands or organs, and either discharged as an excretion or absorbed by the body. A distinction is sometimes made between a true secretion and an excretion. A true secretion is elaborated by certain cells, Known as glands, from substances supplied by the blood, whereas a true excretion already exists in the blood and is merely separated by a particular organ. For instance, the kidneys are frequently said to secret urea, but this is not strictly true. as the urea already exists in the blood, and the function of the kidneys is to separate it and excrete it in urine. On the other hand, the liver secretes bile, which it elaborates from raw materials supplied it by the blood. Other true secretions are saliva, secreted by the parotid, submaxillary, and other salivary glands; milk, secreted by the mammary glands; and tears, secreted by the lachrymal glands.