Black clothing absorbs twice, blue almost twice, red and yellow almost one and a half times, as much heat as white clothing (Exp. 10). Which material protects best from radiant heat? (Exp. 9.) Because large blood vessels are near the surface at the _neck, wrists, and ankles_ very thin or no covering at those points aids greatly in keeping the body cool. High collars, long sleeves, and high shoes are unhealthful in warm climates and in summer. What objection to black shoes in summer? Patent leather? Show how women dress more sensibly in hot weather than men. The =kidneys= are located on each side of the spinal column in the “small of the back” and extend slightly above the level of the waist. They are _bean-shaped organs about four inches long_ (Fig. 26). The kidneys of a sheep or ox closely resemble those of man. They are outside of the peritoneum (Fig. 99) and attached to the rear wall of the abdomen. A large artery (12, colored Fig. 5) goes to each kidney and divides into many capillaries which surround _tubules_ in the kidneys (Fig. 27). The secretion, containing nitrogenous impurities of the blood, is continually being deposited in the tubules, which take it to a _funnel-shaped cavity_ at the inner edge of the kidney (Fig. 26). From this cavity a white tube called the _ureter_ leads down to a storage organ in the pelvis called the bladder. [Illustration: FIG. 26.--SECTION OF KIDNEY. _RA_, renal artery; _Py_, pyramids surrounding hollow space from which the ureter (_U_) leads the secretion to the bladder.] =Changes in Blood in the Kidneys.=--The water holding the nitrogenous waste varies in amount with the amount of water drunk and with the activity of the skin, being less in summer when the perspiration is great. The lungs aid the skin and kidneys in disposing of superfluous moisture. The kidneys have almost the entire responsibility of relieving the body of certain _mineral salts_ and a white crystalline solid called _urea_. This is very injurious if retained, causing headaches, rheumatism, and other troubles. [Illustration: FIG. 27.--PLAN OF A URINARY TUBULE, _Tb_, with artery _A_, and _V_ in _pV_.] THOUGHT QUESTIONS. =Hygiene of the Skin.=--=1.= What kind of a scar is not affected by freckles or tan? =2.= Can a scar on a negro be white? =3.= Does a scar on a child grow in size? =4.= Why is heat most oppressive in moist weather? =5.= How do you account for the shape and location of the usual bald spot? =6.= How does the wearing away of the outer cells of the epidermis contribute to the cleanliness of the body? =7.= Why does the palm of the hand absorb water more rapidly than the back of the hand? =8.= Is it more necessary for mental workers to bathe often or change their clothes often? For physical workers? =9.= Is cotton or woolen clothing more liable to stretch or shrink out of shape or size? To catch fire? To make the skin clammy with moisture? To cost more? To be eaten by moths?