The urine may be considered as one of the most heterogeneous of the animal fluids;[189] and since a knowledge of its composition, and that of the morbid changes of which it is susceptible, must constitute the basis of all our knowledge respecting the formation and cure of calculous affections, the following results of an elaborate analysis by _Berzelius_, are submitted with a view to elucidate our pathological researches. _Animal Principles._│Water 933·00 „ │Urea 30·10 „ │Lithic Acid 1·00 „ │Pure Lactic Acid, Lactate of Ammonia, and │ Animal matters not separable from these 17·14 „ │Mucus of the Bladder ·32 _Alkaline and Earthy│Sulphate of Potass Salts._ │ 3·71 „ │Sulphate of Soda 3·16 „ │Phosphate of Soda 2·94 „ │Phosphate of Ammonia 1·65 „ │Muriate of Soda 4·45 „ │Muriate of Ammonia 1·50 „ │Earthy Phosphates with a trace of Fluate │ of Lime 1·00 „ │Silex ·03 ——————— 1000·00 ——————— Besides the above ingredients, which appear to be essential to healthy urine, Dr. Prout observes that in different diseases it may contain Albumen, Fibrin, and the red particles of the blood; Nitric acid; various acids, which are found to be modifications of the Lithic; Oxalic acid; Benzoic acid; Carbonic acid;[190] Xanthic Oxide; Cystic Oxide; Sugar; Bile; and Pus. It will be necessary in this place to make a few observations upon the nature and habitudes of those principles, which are more immediately active in the production of calculi— 1. _Urea_ is a principle peculiar to urine, and must be regarded as a result of the action of the kidneys upon some of the constituents of the blood, perhaps, as Dr. Prout suggests, upon its albuminous matter. For a long time it was regarded as the peculiar principle upon which the colour and other sensible qualities of the urine depended; Berzelius however has corrected this fallacy, and considers that the Lactic acid, and its accompanying animal matters, are the bodies which impart to this fluid the characteristic smell and colour which distinguish it.[191]