in deposits of urates, crystals of calcium oxalate are often found as well. Uric acid is dibasic, and thus there are two classes of urates-the normal urates and the acid urates. A normal urate is one in which two atoms of the hydrogen are replaced by two of a monad metal like sodium; an acid urate is one in which only one atom of hydrogen is thus replaced. The formulæ would be C5H4N4O3=uric acid CH,NaNO3=acid sodium urate CH2NaNO3=normal sodium urate The acid sodium urate is the chief constituent of the pinkish deposit of urates, which, as we have already stated, is called the lateritious deposit. The quantity of uric acid excreted by an adult varies from 7 to 10 grains (0.5 to 0.75 gramme) daily. The best method for determining the quantity of uric acid in the urine is that of Hopkins. Ammonium chloride in crystals is added to the urine until no more will dissolve. This saturation completely precipitates all the uric acid in the form of ammonium urate. The precipitate is collected on a filter and dissolved in weak alkali. From this solution the uric acid is precipitated by neutralising with hydrochloric acid. The precipitate of uric acid is collected on a weighed filter, dried, and weighed. Origin of Uric Acid.-Uric acid is not made by the kidneys. When the kidneys are removed uric acid continues to be formed and accumulates in the organs, especially in the liver and spleen. The liver has been removed from birds, and uric acid is then hardly formed at all, its place being taken by ammonia and lactic acid. It is therefore probable that ammonia and lactic acid are normally synthesised in the liver to form uric acid. The two conditions which lead to an increase of uric acid in the urine are 1. Increase of meat diet and diminution of oxidation processes, such as occur in people with sedentary habits. 2. Increase of white corpuscles in the blood, especially in the disease known as leucocythæmia. This latter fact is of great interest, as leucocytes contain large quantities of nuclein. Nuclein yields nitrogenous bases (adenine, CH,N5; hypoxanthine, C,H,N,O) which are closely related to uric acid. HIPPURIC ACID Hippuric acid (C,H,NO3), combined with bases to form hippurates, is present in small quantities in human urine, but in large quantities in the urine of herbivora. This is due to the food of herbivora containing substances belonging to the aromatic group--the benzoic acid series. If benzoic acid is given to a man, it unites with glycocine with the elimination of a molecule of water, and is excreted as hippuric acid C.H..COOH+CH,NH,=CH,NH.CO.CH; + H,O 2 [benzoic acid] COOH COOH [hippuric acid] [water] This is a well-marked instance of synthesis carried out in the animal body, and experimental investigation shows that it is accomplished by the living cells of the kidney itself; for if a mixture of glycocine, benzoic acid, and blood is injected through the kidney, their place is found to have been taken by hippuric acid. FIG. 44.-Hippuric acid crystals. CREATININE The creatinine in the urine is nearly all derived from the creatine contained in the meat of the food. There is, however, a small amount in the urine even during starvation: this probably represents a small percentage of creatine in the muscles which has escaped decomposition into urea. The formation of creatinine from creatine is represented in the following equation : C4H9N3O2-H2O=C1H2N2O The small quantity of creatinine in the urine (7 to 10 grains, or 0.5 to 0.9 gramme) will not account for the large quantity of creatine in the muscles (90 grammes). As already stated, it is probably mostly converted into urea. Urea is obtainable artificially from creatine, and it may be that similar reactions occur in the body. The equation that represents the formation of urea from creatine that can be carried out in the laboratory is as follows: C4H9N3O2+H2O=C2H2NO2+CON2H4 The two substances formed are urea and sarcosine. Sarcosine is methyl-glycocine—that is, amido-acetic acid in which one H is replaced It is not found in the body, and so it is broken up, probably in the liver, forming ammonium carbonate and then urea. FIG. 45.--Creatine crystals. FIG. 46.-Creatinine crystals. Creatinine with zinc chloride gives a characteristic crystalline precipitate (groups of fine needles) with composition C,H,N3O.ZnCl2. URINARY DEPOSITS The different substances that may occur in urinary deposits are formed elements and chemical substances. The formed or anatomical elements may consist of blood corpuscles, pus, mucus, epithelium cells, spermatozoa, casts of the urinary tubules, fungi, and entozoa. All of these, with the exception of a small quantity of mucus,' which forms a flocculent cloud in the urine, are pathological, and the microscope is chiefly employed in their detection. The chemical substances are uric acid, urates, calcium oxalate, calcium carbonate, and phosphates. Rarer forms are leucine, tyrosine, xanthine, and cystine. We shall, however, here only consider the commoner deposits, and for their identification must use the microscope and certain chemical tests as well. Deposit of Uric Acid. This is a sandy reddish deposit resembling cayenne pepper. It may be recognised by its crystalline form (fig. 43, p. 98) and the murexide reaction. The presence of these crystals generally indicates an increased formation of uric acid, and, if exces Recent observers state that urinary mucin, like bile mucin, is not true mucin, but a nucleo-albumin. sive, may lead to the formation of stones or calculi in the bladder. The way in which uric acid is split off from the urates is of great interest to pathologists, and will be found fully discussed in Sir W. Roberts's Croonian Lectures.1 Deposit of Urates. This is much commoner, and may, if the urine is concentrated, occur in normal urine when it cools. They are generally found in the concentrated urine of fevers; and there appears to be a kind of fermentation, called the acid fermentation, which occurs in the urine after it has been passed, and which leads to the same result. The chief constituent of the deposit is the acid sodium urate, the formation of which from the normal sodium urate of the urine may be represented by the equation- 2C2H2Nа2NO + H2O + CO2 = 2C5H2NaNO3 + Na2CO3 5 2 [normal sodium urate] [water] [carbonic 4 [acid sodium This deposit may be recognised as follows:- [sodium carbonate] 1. It has a pinkish colour; the pigment called uro-erythrin is derived from the pigment of the urine, but the exact relationship of the two is not known. 2. It dissolves upon warming the urine. 3. Microscopically it is usually amorphous, but crystalline forms similar to those depicted in the next two figures may occur. گا۔ FIG. 47.-Acid sodium urate. FIG. 48.-Acid ammonium urate. Crystals of calcium oxalate may be mixed with this deposit FIG. 49.-Envelope crystals of calcium oxalate. (see fig. 49). Deposit of Calcium Oxalate. This occurs in envelope crystals (octahedra) or dumb-bells. It is insoluble in ammonia, and in acetic acid. It is soluble with difficulty in hydrochloric acid. Deposit of Cystin.-Cystin (C6H12N2S2O1) is recognised by its colourless six-sided crystals (fig. 50). they occur only in acid urine, and they may form concretions or calculi. These are rare: Published by Smith, Elder, & Co. London, 1892. Deposit of Phosphates.-These occur in alkaline urine. The urine. may be alkaline when passed, due to fermentative changes occurring in the bladder. All urine, however, if exposed to This the air, will in time become alkaline owing to CON2H1 + 2H2O = (NH4)2CO3 [urea] 4 The ammonia renders the urine alkaline and precipitates the earthy phosphates. The FIG. 50.-Cystin crystals. chief forms of phosphates that occur in urinary deposits are 1. Calcium phosphate, Ca3(PO4)2; amorphous. 2. Triple or ammonio-magnesium phosphate, MgNH,PO,; coffinlids and feathery stars (fig. 51). 3. Crystalline phosphate of calcium, CaHPO4, in rosettes of prisms, in spherules, or in dumb-bells (fig. 52). Triple Phosphate FIG. 51.-Triple phosphate crystals. FIG. 52.-Crystals of phosphate of lime (stellar phosphate). 4. Magnesium phosphate, Mg,(PO4)2+22H2O, occurs occasionally, and crystallises in long plates. All these phosphates are dissolved by acids, such as acetic acid, without effervescence. They do not dissolve on heating the urine; in fact, the amount of precipitate may be increased by heating. Very often neutral or alkaline urine will become cloudy when boiled: this may be due to albumin or to phosphates. It is very important to distinguish between these two, as albuminuria is a serious condition. They may be |