excretion of urates, or lithates (λίθο, stone), as they used to be called, because the “stones” which are found in the bladder consist largely of uric acid. From this it appears that faulty distribution and inadequate excretion have more to do with the development of the symptoms of gout than over-production. In a previous chapter (p. 140) we gave as the predominant cause of gout acid fermentations in the stomach. It does not, by any means, follow, however, that we were right in correlating imperfect digestion with an excessive formation of uric acid. It may well be that the gouty symptoms to which hampered peptic digestion gives rise are due in larger measure to a disturbance of the composition of the body-fluids which renders them unfit to carry uric acid to the kidneys in such a form, or in such relation to the fluid in which it is dissolved, as will insure its escape into the urinary tubules. The interference with the efficient working of the system caused by accumulation in it of uric acid gives a particular interest to all that is known regarding the nature and origin of this substance. Uric acid has the formula C₅H₄N₄O₃. It is a more complicated and a more stable body than urea. The deposits of guano in Peru contain uric acid (the excrement of birds) which has remained practically unchanged for years—for centuries, perhaps. Its chemical nature is not completely understood. It can be readily made to yield urea; and it can be formed by conjugating urea with a nucleus derived from lactic acid (_cf._ p. 13). Its formula is therefore commonly represented as that of a diureide—a substance containing two urea radicles: { HN——CO { | CO { C——NH } { | } CO { HN——C——NH } But notwithstanding this inclusion in its molecule of two radicles of urea, it is safe, when one thinks of the contrast between urea and uric acid, to lay stress, in the case of the former, on the binding of nitrogen to hydrogen; in the case of the latter, on the binding of nitrogen to carbon. Uric acid is soluble with difficulty; it crystallizes in rhombs. It forms salts, normal and acid. Those which appear in the urine are always acid salts. As a treatment for “stone,” lithia water has long had a reputation which it probably deserves, the acid urate of lithium being the most soluble salt of uric acid which the kidney can secrete. When uric acid is in excess in urine, brown crystals of uric acid are deposited as “gravel” soon after it is passed. Even when not in excess, uric acid crystals appear after a sufficient time. In other cases uric acid, when in excess, is thrown down in the form of a cloud of acid urates of sodium and other bases, which renders the urine turbid. These urates are redissolved when the water is warmed.