Uric acid and urate of sodium are the direct exciting causes of gout. By repeated experiments it is demonstrated that the production and elimination of urate of sodium is influenced both by food and certain drugs. When the diet was chiefly of meat or animal food the elimination was diminished, eauging the uratcs to accumulate in the system, while the reverse occurred under a vege table diet. A. Haig (Brit. Med. Jour., July 7, 'SS).
The theory must be considered as proved which attributes the formation of uric acid in the body to a process of teucotysis, following ou a leucocytosis. A review of the literature upon tissue necrosis in gout leads the writer to state definitely that the process is caused by a poison, probably a nucleic acid, acting in a similar way to that in which tissue necrosis is caused by lead in plumbism. Froelich (Jour. Amer. Med. Assoc., Jan. 3, '97).
Both chemico-physiological and clin ical evidence point clearly to a defective oxidation as the chief predisposing factor in causing the pathological lesions of rheumatism and gout. This may be due to taking into the body more oxidizable food products than the normal system can fully oxidize, or a diminution in food, especially of a poor quality, may result in malnutrition and anremia such that the food does not encounter suffi cient oxygen for its perfect reduction. W. II. Porter (N. 17. Med. Jour., Mar. 24, 1900).
While it is easy to increase the quan tity of urea excreted in twenty-four hours by the ingestion of large quantities of proteids, the excretion of uric acid is not much influenced in that way. Wein traub, Umber, and Kiihne have demon strated that the excretion of uric acid may be increased to 2 or 2.5 grammes in twenty-four hours by giving large quan tities of nuclein,—for instance, 500 grammes of the thymus gland,—whereas the normal excretion of uric acid varies from 0.4 to 1 gramme per day.
The augmented formation of uric acid will, of course, lead to a temporary uri cminia, which usually does not cause any morbid symptoms, but is only character ized by an extraordinary increase of the excretion of uric-acid compounds in the urine.
By chemical investigation of the gouty deposits, these have been found to con sist of an acid compound of uric acid with soda, the so-called biurate, and it has commonly been stated that this was also the composition of uric acid circu lating with the blood. Roberts has re
cently thoroughly investigated this ques tion.
[Roberts's results have quite over thrown this theory. In text-books on chemistry, uric acid is described as a dibasic acid, which can form a neutral (M,U) salt and an acid salt biurate (MHU). The neutral salt can only be prepared by dissolving pure uric acid in a solution of caustic soda and evaporating to dryness, without the entrance of air. It can never exist in the body and we need not refer to it again. The biurate is the chief compo nent of the tophi and was supposed also to be contained in the blood and the urine, and under circumstances to be pre cipitated as a brick-dust deposit. By ex amining this sediment Roberts found it to be an unstable compound which easily decomposes into uric acid and a soluble comporind; by chemical investigations of different order it was demonstrated that the deposit formed by the urine cannot be regarded as a biurate, but is a quadri urate: i.e., a compound of four equiva lents of uric acid with one equivalent of soda or potash; its chemical formula is consequently II,u, MHu. This quadri urate is a very unstable compound, liable to be decomposed into biurate and uric acid; this decomposition is effected by adding distilled water to the sediment and by many other fluids. The gouty tophi consist of biurate, but this salt is almost insoluble in serum,—even, at the body-temperature, only in the propor tion of 1 in 10,000. F. LEvlsox.] The researches of Roberts establish that, normally, uric acid exists in the blood as a quadriurate; under special cir cumstances the quadriurate may be trans formed in the blood to a biurate, which gives rise to the deposition of this com pound in different parts of the body; the more uric acid is dissolved, the more quickly occurs the formation and deposit of biurate, but in all cases the uric acid cannot remain long in solution; if it is not quickly eliminated by the kidneys, transformation of the quadriurate and deposition of biurate is the consequence.