Fresh green vegetables and acid fruits may be taken. Potatoes contain calcium, but because they contain much more potassium, which lessens the liberation of calcium, they may also be used. For foods rich in calcium which should be avoided see page 219. Foods causing calcium oxalate deposits should be avoided as they may cause the formation of gall-stones. For a list of these see p. 219. Meat, if taken, must be lean and eaten only once a day. Beef and chicken are the preferable meats. Fresh fish may be used. Alcohol must not be taken and coffee and tea must be limited in strength and quantity. Active exercise must be practiced daily and full elimination secured from the bowels. The person afflicted with gall-stones must not sit too long or in a cramped position. The presence of fat in the duodenum increases the flow of pancreatic juice which, in turn, stimulates the flow of bile, so olive oil is often recommended in case of gall-stones. It is questionable whether it is of benefit, because, as stated, much fat upsets the liver. Watch the water supply. Hard water which contains lime should be boiled to precipitate the calcium. _DERANGEMENTS OF THE KIDNEYS_ The office of the kidneys is to eliminate from the system certain nitrogenous elements in solution; the work of the kidneys, in most conditions, is aided by copious drinking of water. The influence exerted on the function of the excretory organs by the components of the food has not been given the attention it merits. If the fluids are not taken in sufficient amount and much animal food is eaten, the urine becomes more concentrated and may irritate the kidneys or the bladder and give rise to calculi (kidney stones) or to the deposit of uric acid. Watery vegetables, juicy fruits, milk, water, and most beverages, by increasing the output of urine, lessen its acidity and density. A diet limited to certain articles of food by the likes or dislikes of the individual, as the starches and sugars, too large consumption of acid fruits or too fatty foods may cause the appearance in the urine of abnormal amounts of various substances, as sugar, phosphates, calcium oxalate, or fatty acids. Acid fruits in moderation aid digestion and favor suitable elimination, but when eaten to excess, as lemons, taken two or three or more a day by those striving to reduce flesh, the urine is increased in acidity, and irritation of the bladder may ensue. Too great an amount of food tends to overwork the kidneys as well as the liver and various derangements result; these must be treated dietetically as well as by medicine. [Sidenote: Acute Nephritis] In inflammation of the kidneys (nephritis), the secretion of urine is lessened or may cease. The kidneys and digestive system must not be overworked and all food must be eliminated save milk until the kidney function is restored. It may be diluted with lime or Vichy, or skimmed milk or buttermilk may be used.