The excretion of lime by the kidneys is often, especially in those who metabolise purins badly, complicated by its combination with oxalic acid, and a well-recognised group of symptoms, including headache, backache, listlessness, depression, and sometimes dysuria, is often to be met with in such subjects. This condition has been termed oxaluria, and it has been conjectured that food-stuffs containing oxalic acids are particularly to be blamed for its origin. Hence such foods as rhubarb, spinach, sorrel, tomatoes and strawberries, which are stated to contaiu large quantities of oxalic acid, are shunned by sufferers from this ailment, and even figs, plums, potatoes, beetroot, gooseberries, tea, coffee, and cocoa are placed upon the proscribed list by enthusiastic dietists.

But it has been demonstrated that it may owe its inception to other circumstances, such as fermentative dyspepsia, from an excess of carbohydrates in the diet, or at least from carbohydrate decomposition in the alimentary canal under conditions not yet clearly apprehended, and that even the acidity of the gastric juice has much to do with the absorption of oxalates from the food. General practitioners are well aware of the fact that subjects of hyperchlorhydria have an idiosyncrasy for excessively acid fruits and vegetables, and that acids of all kinds are apt to disagree with them, while alkalis suit them, or in any case give them temporary comfort. For those who refuse to deny themselves the pleasure of eating stewed rhubarb, even where experience has taught them that its ingestion is almost immediately followed by an effusion into the joints, it may be comforting to know that if it be soaked for two hours prior to cooking in a solution of carbonate of soda, this water discarded, and then a very large pinch of bicarbonate of soda be added to the water in which it is cooked, immunity from the usual disastrous consequences may be expected.

The appearance of oxalate of calcium in the urine is not sufficient reason for diagnosing oxaluria, because it is a constant constituent of human urine, although it may not always deposit in crystalline form. It is only when an excessive quantity is present in the urine that the designation oxaluria is correctly applied, and in such circumstances inquiry must be instituted to discover whether its origin be exogenous, i.e., produced from the food introduced into the alimentary canal, or endogenous, i.e., due to some metabolic disturbance. Very little, however, is known about the method of its endogenous production, but it is always important to note whether crystals of oxalate of calcium are present in newly passed urine, or whether they deposit after it has been passed. Klemperer and Tritschler have demonstrated that the acid phosphates of calcium, sodium, and magnesium - especially the last, and also other salts of magnesium, such as the sulphate - exercise a solvent action on calcium oxalate.

The treatment of oxaluria, with the object of preventing the formation of concretions or dissolving those already formed, resolves itself into (1) diminution of the excretion of oxalic acid; (2) increasing the solubility of oxalate of lime in the urine. The former indication is met by expunging from the dietetic list all articles containing oxalic acid, such as tea, rhubarb, sorrel, spinach, and the avoidance of gelatine, which undoubtedly increases its output. Milk, white of egg, and all fats except yolk of egg should likewise be avoided. Acidity in the alimentary canal should also be diminished to prevent as far as possible absorption.

To fulfil the second indication, foods containing magnesium, such as rice, peas, farinaceous foods, and coffee, should be substituted; small doses of sulphate of magnesium should be exhibited, so that magnesia may be in excess in the urine; and citrate of potash not only prevents the formation of oxalate of lime crystals, but acts as a diuretic and so increases the volume of fluid available for solution. Acting on Klemperer's hint, acid phosphate of soda has more recently been recommended as a solvent.

It is probably futile to attempt the adoption of an acalcic diet in oxaluria, for no diet can be planned that would reduce the calcium-content so low as to be insufficient to combine with the few centigrams of oxalic acid excreted daily. Even in cases where enormous quantities of oxalate of calcium crystals are excreted in the urine, as amongst the Manipuris of Eastern Bengal, whose diet is entirely confined to vegetables and fruit, and whose drinking water is prominently deficient in calcium salts, it is quite evident that excess of calcium is not necessary for the formation of the oxalate of lime. Some other factor is always in operation, and therefore, in addition to the measures already suggested, the rational treatment consists in improving the metabolism of carbohydrates so as to inhibit the formation of endogenous oxalic acid.

The salts of magnesium, fluorine, iodine, or sulphur, although doubtless important constituents of the body, are not of special significance in relation to any dietetic system.