The urine of jaundice has invariably a peculiar tint, ranging from a saffron-yellow to a dark olive-green, or almost black hue. It must not be forgotten that the colour of normal urine varies with the degree of concentration. Where little is passed, being of a high, where much is passed, of a pale colour; the depth of colour depending on the degree of dilution of the urohæmatine. Again, it must also be remembered that there are many diseases, which change the colour of urine very materially, some only deepening, others actually changing the tint. Foods, and medicines also, {56} alter the colour of the renal secretion. Rhubarb, and santonine give to it a saffron hue, arsenious acid gas a black colour. Bearing in mind these facts, one would hesitate before giving a decided opinion as to the presence or absence of icterus from a mere inspection of the urine. For this reason, it is generally recommended in cases of jaundice to pour a little of the urine on a white plate, and watch the play of colours produced by strong nitric acid. This method, however, is not always satisfactory, for the play of colours depends on the different stages of oxidation through which the pigment passes, and other animal pigments, besides biliverdine, unfortunately act in a somewhat similar manner. A very simple, and more convenient way of testing the pigment without changing its physical characters, is to separate it in combination with uric acid. This is readily done by simply acidulating the urine with a few drops of hydrochloric acid, and setting it aside for twenty-four hours to crystallize. The white uric acid in crystallizing takes up the colouring matter, and assumes the hue of the pigment present in the urine. I have thus obtained crystals of all the different hues from a bright golden yellow tint through the intervening shades of red, brown, blue, olive, to a dark, almost black colour. This experiment {57} has another advantage, for if we take a measured quantity of urine, and collect, dry, and weigh the uric acid obtained from it, we can readily calculate the total quantity passed in the twenty-four hours, and thereby assist in diagnosing the presence or absence of malignant disease of the liver, as I shall afterwards have occasion to point out.