Dr. Bird says that when a deposit suspected to contain eystine is examined, it should be washed with boiling water to remove the urates and any crystals of common salts which might be present, and then placed in a drop of water on a slip of glass under the microscope. Crystals of cystic oxide will then be readily distinguished, by their presenting one or other of two forma under which it oceurs. Its the first of these it appears under the form of tolerably regular six-sided tables, sometimes transparent throughout, but more generally opaque in the centre. In the second it occurs as roundish tables, opaque in the oentre, and often quite so, somewhat crenate at. the edges.
Cystic oxide may be distinguished by its solubility in all:alines and most acids, and by the characteristic odour it yields when burnt. It is however very little soluble in acetic acid ; hence when cystic oxide exists in the urine, it may be readily precipitated from that fluid by vinegar.
Lewin has also been found in the urine. This substance exists normally in the spleen, liver, pancreas, and thymus glaud. It has been found present in the urine in disease of the liver.
Tyro:in, Hypoxonthin, and tannin have been also found in the urine.
Sugar does not exist in healthy urine, but in certain states of disease it is found in large quantities. Sugar of diabetic urine differs in appearance from common sugar, and approaches in its properties to the sugar of grapes, with which it is identical in composition. Urine containing sugar is generally pale-coloured, of specific gravity above P030, and its natural ingredients are often relatively much diminished in quantity. This substance is present in the disease called diabetes. [DIABETES.] Sugar ie found temporarily present in the urine, and' is supposed to be produced by a casual absence of oxidation. Thus it has been observed in the urine after temporary injuries of the head. It has also been said to occur in all cases in which respiration is impeded, emphysema, hooping-cough, epilepsy, hysterics, &c.
(layering matters of various kinds have been found in the blood. Prout first observed indigo in the urine. Hassell examined this sub ject, and found indigo present in several kinds of urine. Heller has also discovered a blue colouring matter in urine, which he calls mox anthin. This substance is closely related to indigo, and probably both are produced by the same series of changes. A green pigment and a pink pigment, called euroerythrin, have also been found in urine in various forms of disease. Bile pigments are not unfrequently present in the urine of even healthy persons, and are constantly present in those affected with jaundice.
Various acids besides the normal acids have been found in urine. Such are the bile acids, taurocholic and glycocholie, acetic, lactic, butyric, and nitric acids. Sulphuretted hydrogen is also occasionally
detected in the urine when first passed.
Of the abnormal sediments in the urine, the most frequent and Interesting in the salt of lime with :— Oxalic Acid—Oxalate of Lime. Oxalic acid is never found in healthy urine, although, according to the important investigations of Dr. Golding Bird, deposits of oxalate of lime are of common occurrence. Where the acid does not result from the peculiar character of the ingests containing it, as rhubarb or sorrel, the occasion of this morbid deposit is the formation of oxalic acid in the living body, possibly from some undue oxidation of carbon within the kidney. So strong is the affinity between lime and oxalic acid, and so great the insolubility of the resulting compound, that the addition of a very minute quantity of oxalic acid occasions in the urine a precipitate of oxalate of lime, because the oxalate, unlike the phosphate of this earth, is not at all soluble in the natural acid of the secreted fluid. Dr. G. Bird says, that when deposits of oxalate of lime exist, the urine is acid ; in tiut varying from a pale straw colour to deep amber, sometimes nearly limpid, much more generally containing a copious deposit of urate of ammonia of a very pale colour, rarely being tinged with pink ; and frequently mixed with uric acid and numerous fragments of epithe lium; the specific gravity generally- exceeds the average density of healthy urine, but sometimes is below it, varying from to 1.029. An excess of urea is frequently present, so that when the urine is above the density of 1.020, it crystallises very quickly after the addi tion of an equal bulk of nitric acid. When the urine contains no urate of ammonia the deposit of oxalate of lime, on account of its transparency, is generally nearly imperceptible ; but on decanting the superabundant fluid, after a few hours' repose, and placing a few drops of the lowermost layers in a capsule, a white crystalline sediment is very readily distinguishable, and this, when examined under the micro scope, presents a very beautiful appearance. The crystals are of three forms, octahedra, hour-glass or dumb-bell bodies, and small flattened disc-like bodies sometimes round but more frequently elongated, which may be the beginning of the dumb-bell crystals. The octahedral crystals are the most common. Bird and others have attributed a variety of symptoms to the presence of oxalic acid in the system, but Lehmann and Scherer have denied that any connection whatever can be traced between the symptoms described and the appearance of oxalate of lime in the urine. Such a view is also supported by those writers who maintain that the oxalic acid is not formed in the blood at all, but is the result of changes in other constituents of the urine after it has passed from the bladder.