The term common integument comprehends ordinary skin with its covering of hair and variety of skin glands as well as more specialized parts such as claws, hoofs, and horns.
The skin completely encloses the body and blends with the mucous membranes at the various natural openings. In its common form it protects against surface wear and tear and invasion by microorganisms, plays an important part in thermoregulation (p.
357), and, being practically impermeable to water, prevents the body from drying out (with the accompanying loss of electrolytes and other vital substances); conversely, it prevents excessive water uptake in aquatic mammals. Certain lipid substances can penetrate skin and are used (in the form of ointments) as vehicles for administration of medication.The color of skin (and hair) depends partly on the presence of pigment granules in certain component cells. These protect against ultraviolet radiation and are related to the ability to reflect solar heat, which may raise body temperature; their effects partly explain why skin and coat color affects the adaptability of animals to life in sunny climates. The color of naked and nonpigmented areas is also affected in various ways by the blood in the vessels that perfuse its deeper layers; blushing in humans provides the most obvious example of such effects, but the pallor of anemia or shock, the blue tint (cyanosis) that indicates oxygen lack, and the yellow (icterus) of jaundice are of greater veterinary relevance. Very spectacular color changes, such as that for which the chameleon is famous, do not occur in mammals, although mention may be made of the garish coloration of the skin of the mask and perineum of male mandrills and related monkeys.