One part of each of these solutions and two parts of water are mixed and used for the test. The bromin solution must be kept in a tightly stoppered bottle or it will rapidly lose strength. * * * * * 5. Uric Acid.--Uric acid is the most important of a group of substances, called _purin bodies_, which are derived chiefly from the nucleins of the food and from metabolic destruction of the nuclei of the body. The daily output of uric acid is about 0.4 to 1 gm. The amount of the other purin bodies together is about one-tenth that of uric acid. Excretion of these substances is greatly increased by a diet rich in nuclei, as sweetbreads and liver. Uric acid exists in the urine in the form of urates, which in concentrated urines are readily thrown out of solution and constitute the familiar sediment of "amorphous urates." This, together with the fact that uric acid is frequently deposited as crystals, constitutes its chief interest to the practitioner. It is a very common error to consider these deposits as evidence of excessive excretion. Pathologically, the greatest increase of uric acid occurs {68} in leukemia, where there is extensive destruction of leukocytes, and in diseases with active destruction of the liver and other organs rich in nuclei. Uric acid is decreased before an attack of gout and increased afterward, but its etiologic relation is still uncertain. An increase is also noted in the uric-acid diathesis and in diseases accompanied by respiratory insufficiency. _Quantitative Estimation_.--The following are the best methods for ordinary clinical purposes, although no great accuracy can be claimed for them. [Illustration: FIG. 21.--Ruhemann's uricometer.] * * * * * Cook's Method for Purin Bodies.--In a centrifuge tube take 10 c.c. urine and add about 1 gm. (about 1 c.c.) sodium carbonate and 1 or 2 c.c. strong ammonia. Shake until the soda is dissolved. The earthy phosphates will be precipitated. Centrifugalize thoroughly and pour off all the clear fluid into a graduated centrifuge tube. Add 2 c.c. ammonia and 2 c.c. ammoniated silver nitrate solution. Let stand a few minutes, and revolve in the centrifuge until the bulk of precipitate _remains constant_. Each one-tenth cubic centimeter of sediment represents 0.001176 gm. purin bodies. This amount may be regarded as uric acid, since this substance usually constitutes nine-tenths of the purin bodies and the clinical significance is the same. _Ammoniated silver nitrate solution_ is prepared by dissolving 5 gm. of silver nitrate {69} in 100 c.c. distilled water, and adding ammonia until the solution clouds and again becomes clear.