URIC ACID. 779 



quantity of urea. Some of the products of the metamorphosis of the 

 muscular tissue, such as creatin, xanthin, and sarcin, have affinities 

 with uric acid. Lastly, in a state of rest, the quantity of uric acid ex- 

 creted increases, whilst the urea ultimately diminishes, the reverse 

 being the case from exercise. 



The quantity of uric acid excreted daily, has been estimated at 

 from 8J to 15 grains ; but this, like the quantity of urea, varies very 

 much, most markedly according to the amount of nitrogenous food 

 which is taken, and less so according to the age and sex. Its quan- 

 tity is lessened by exercise. With animal diet, its quantity is said to 

 be 4.5 grains, and with vegetable diet, only about 1.5 grain daily. 

 (Haughton.) In the urine, it is either combined with soda, forming 

 the urate of soda, which is held in solution, or else it is dissolved by 

 the alkaline phosphate of soda. Being less soluble than its salts, uric 

 acid is quickly precipitated by acids, and moreover, being itself less 

 soluble in cold than in warm water, it is commonly precipitated from 

 normal urine after cooling. This may be partly from the diminished 

 solvent power of the cooler fluid, and partly from the occurrence of 

 the lactic acid fermentation. Uric acid is then precipitated and de- 

 posited, either in an amorphous powder, or in fine crystals of peculiar 

 forms, often tinged with coloring matter. The crystals are sometimes 

 little flattened rhomboids, sometimes they resemble a coffin or a barrel, 

 and sometimes they are almost spherical. It forms the most common 

 urinary sediment, and the most frequent kind of renal or vesical cal- 

 culus or stone in the kidney or bladder. Hence it is also named lithic 

 acid (hdoq, a stone). Urate of soda constitutes the solid urinary ex- 

 cretion of Serpents, and is also present, in large quantity, in the white 

 pasty portions of the dejecta of the flesh and fish-eating Birds, such 

 as the hawks and owls, the penguins and other sea-birds. Hence it 

 exists in large quantity in guano. It may be obtained pure from hu- 

 man calculi, or from the solid excretion of the serpent, by dissolving 

 the urate in those substances in a hot solution of caustic potash, and 

 reprecipitating it from the filtered fluid, by means of another acid. 

 The precipitate is a white powder, composed of colorless rhomboidal 

 scales ; it is almost insoluble in cold water, and only slightly so in hot, 

 and is absolutely insoluble in alcohol and ether ; it is soluble in alka- 

 line solutions, and very readily in solutions of lithia. From all these 

 solutions, it is immediately reprecipitated, even by feeble acids. 

 Heated nearly to dryness with nitric acid, uric acid turns red, and, on 

 the addition of ammonia, a beautiful purple substance, named murexid, 

 is formed, a reaction which constitutes a test for uric acid. The fact 

 that uric acid is a less perfectly oxidized compound than urea, ex- 

 plains, perhaps, its formation in excess under certain conditions, as, 

 e. <?., when the quantity of tissue metamorphosed, or the quantity of 

 food taken, is greater than the supply of oxygen can convert into 

 urea, as, e. </., in acute inflammations, rheumatism, and gout, in all 

 which diseases, large quantities of uric acid deposits, or of urates, are 

 thrown down from the urine, which is loaded at critical periods, after 

 the climax of the attack. At the onset of the gout, the uric acid 

 sometimes nearly, or entirely, disappears from the urine ; it may then 



