Ruhemann's Method for Uric Acid.--The urine must be slightly acid. Fill Ruhemann's tube (Fig. 21) to the mark _S_ with the indicator, carbon disulphid, and to the mark _J_ with the reagent. The carbon disulphid will assume a violet color. Add the urine, a small quantity at a time, closing the tube with the glass stopper and shaking vigorously after each addition, until the disulphid loses every trace of its violet color and becomes pure white. This completes the test. The figure in the right-hand column of figures corresponding to the top of the fluid gives the amount of uric acid in parts per thousand. The presence of diacetic acid interferes with the test. _Ruhemann's reagent_ consists of iodin and potassium iodid, each 1.5 parts; absolute alcohol, 15 parts; and distilled water, 185 parts. * * * * * B. ABNORMAL CONSTITUENTS Those substances which appear in the urine only in pathologic conditions are of much more interest to the clinician than are those which have just been discussed. Among them are: proteids, sugars, the acetone bodies, bile, hemoglobin, and the diazo substances. The "pancreatic reaction" and detection of drugs in the urine will also be discussed under this head. 1. Proteids.--Of the proteids which may appear in the urine, serum-albumin and serum-globulin are the most important. Mucin, albumose, and a few others are found occasionally, but are of less interest. (1) Serum-albumin and Serum-globulin.--These two proteids constitute the so-called "urinary albumin." They usually occur together, have practically the same {70} significance, and both respond to all the ordinary tests for "albumin." Their presence, or _albuminuria_, is probably the most important pathologic condition of the urine. It is either _accidental_ or _renal_. The physician can make no greater mistake than to regard all cases of albuminuria as indicating kidney disease. _Accidental_ or _false albuminuria_ is due to admixture with the urine of albuminous fluids, such as pus, blood, and vaginal discharge. The microscope will usually reveal its nature. _Renal albuminuria_ refers to albumin which has passed from the blood into the urine through the walls of the kidney tubules or the glomeruli. It probably never occurs as a physiologic condition, the so-called "functional albuminuria" being due to obscure or slight pathologic changes. Renal albuminuria may be referred to one or more of the following causes. In practically all cases it is accompanied by tube-casts. (_a_) _Changes in the blood_ which render its albumin more diffusible, as in severe anemias, purpura, and scurvy. Here the albumin is small in amount.