Oxalic acid is maintained in solution in the urine, as calcium oxalate (CaC,O,), in small quantities by the acid phosphates of the urine. Oxalic acid (H,C,O.) was first obtained from urine by Schunck in 1867. Perhaps one grain is secreted daily, however, some have reported seven grains daily. Oxalic acid (H.CO) and calcium (Ca) have a

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FIG. 1.

(Schede). Calculus. A- Nucleus of uric acid, periphery of phosphates. B-Nucleus of uric acid, periphery calcium oxalate. C-Nucleus of uric acid, middle layer calcium oxalate and periphery phosphates.

FIG. 2.-(Byron Robinson). Crystals of calcium oxalate. The double pyramid form, octohedron, or envelope-shape; the minor forms on dumb-bell, kidney, and other forms.

strong affinity for each other, and the diad Ca displacing the acid base H2 forms CaC,2O4. Purified oxalic acid is dissipated by heat below 350° F. If calcium oxalate be found in the urine within twelve to fortyeight hours after evacation, it shows that there is an excess of oxalic

acid in the system. This may arise from the nature of food or from imperfect oxidation. Oxalates frequently form calculi and more frequently produce structural renal changes. In the majority of the subjects CaCO crystals are formed after the urine leaves the body.

The habit of body which favors the formation and deposition of oxalates is termed oxaluria or oxalic diathesis, which scarcely, in my opinion, merits the classification of a disease, but rather is the results of defective methods of living.

Idiopathic oxaluria occurs in illdefined morbid states due to excessive secretion of oxalic salts. Idiopathic oxaluria is a condition where excessive oxalic acid is associated with vague pain and dragging in the lumbar region.

Vicarious oxaluria is a distinct alteration between the amount of sugar and calcium oxalate excreted. Oxaluria occurs chiefly in association with lithemia, that is, with uric acid and urate crystals.

Alimentary oxaluria is a condition from injesting food containing excessive quantities of oxalic acid which appears in excessive quantities in the urine. It is in contra distinction to oxaluria from oxidation. Endogenous oxalic acid appears in increased quantities in association with diabetes mellitis, in organic hepatic disease and in defective oxidation. In subjects of jaundice the crystals have a yellowish color. The origin of oxalic acid is both exogenous, extrinsic (food) and endogenous, intrinsic (oxidation). Dr. Leard has shown that if calcium hydrate (Ca2HO, lime water) be administered in the evening there will be an abundant deposition of calcium oxalate (CaC2O4) crystals in the urine in the morning. Oxalate of calcium crystals are deposited in the urine if oxalic acid be administered in one-half grain doses and also the crystals may be found in the urine many days subsequent to suicidal attempts with oxalic acid. Calcium oxalate occurs chiefly in acid urine but may occur in alkaline or neutral urine. Calcium oxalate crystals possess no special pathologic signification as the factors which decide their formation is not known. At present no known disease induces oxaluria.

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Calcium oxalate may be found in the urine of both healthy and diseased subjects. In health calcium oxalate depends on the ingredients of the ingested food. Oxalate of calcium crystals are frequently found in diseased conditions-especially in disturbances of the tractus intestinalis. Large quantities of calcium oxalate may occur in the urine after ingesting certain vegetables (as beans, carrots, and asparagus). The quantity of oxalate crystals is no indicator of the amount of oxalic acid in the urine, for the urine may contain considerable oxalic acid with a minimum quantity of precipitated oxalic crystals. Calcium oxalate is frequently associated with pathologic changes in the urine. It appears that calcium oxalate (CaC2O,) occurs most abundantly in association with urine rich in other forms of excessive urinal secretions or solids.

Calcium oxalate is held in solution by monophosphate; it is not soluble in the diphosphates. Hence, when uric acid is precipitated from the urine, the acidity of the urine decreases and the monophosphates are

FIG. 3 (Byron Robinson) presents a shadow of nine isolated chemically pure crystallized salts found in urine (1-9), lying on a segment of pasteboard box, and (I to IX) is the same series of salts enclosed in gelatine capsules (1-13) x-ray shadows of hepatic calculi. III and 3, calcium oxalate.

converted into diphosphates CaCO, will crystallize. Calcium oxalate is therefore found in acid urine. Calcium oxalate crystals form after the urine is voided and is hastened by cold. Primary oxalate crystals irritate the tractus urinarius. The mechanical irritation may be so trau

matic as to produce hæmorrhage and catarrh, with accompanying pain and painful micturition.

The clinical signification of excess of oxalic acid as oxaluria is indefinite. If oxaluria be not alimentary, it perhaps indicates deviation from the usual oxidation, indicating incomplete metabolism of uric acid (H2CH2NO). Excess of calcium oxalate (CaC,O,) in the urine. does not always indicate a clue to the existing pathologic conditions. However, it should instigate the clinician to investigate for complicacations. Oxalate crystals are liable to appear in diabetes mellitus, catarrhal jaundice, and spermatorrhea. Calcium oxalate crystals are found in 25 per cent. of urines in twelve to twenty-four hours after voiding. If found in fresh urine, some irritation of the urinary passages probably exists. The crystals are frequently suspended in a cloudy mucous sediment. Calcium oxalate crystal are apt to appear in the urine of the patient afflicted by fluid diarrhoea. In this state oliguria favors the increase of calcium oxalate crystals. Calcium oxalate tends to crystalize and form a nucleus when in contact with any object; for example, on fine threads or shreds of mucous.

Oxalate of calcium crystals occur more frequently in the urine in summer months during the greatest evaporation from the body. In subjects of oxaluria where crystals are present in abundance they may occasionally cause calculus. Oxalates occur in nature in the juices of some plants, as wood sorrel (oxalis acetosella, which yields the salt of sorrel-KHC,04, acid potassium oxalate), and rhubarb (rheum), common dock (rumex communis), and certain lichens. The form is chiefly as sodium, potassium, and calcium salts.

The carbon of many substances yields oxalic acid, as well as fat, sugar, and starch. Oxalic acid is extensively distributed in the vegetable kingdom in the form of potassium, sodium, or calcium salts. Oxalic acid acts as a reducing agent, decolorizing solutions of permanganitis, and precipitates gold and platinum from their solutions. Oxalic acid taken in large doses is a poison. Antidotes to oxalic acid are calcium carbonate (CaCO) and calcium hydrate (Ca, HO), lime water, which should be administered, producing an insoluble calcium oxalate (CaC2O1).

Alkalies should not be administered, as all alkali oxalates are soluble. In regard to calcium oxalate crystals, an important and suggestive factor occurs when a subject eats vegetables containing oxalic acid, an abundant deposition of calcium oxalate crystals may be observed in the urine. These data lend a suggestive key to the treatment of excessive calcium oxalate in the urine.

Oxalic acid is an intermediate product between uric acid and urea ; the process resting an oxidation and with minimum oxidation it results in oxaluria, for example, in cardiac and pulmonary diseases (defective oxidation) oxaluria is frequent. Nervous diseases are frequently accompanied by oxaluria; which precedes or follows the other is difficult to

determine.

Oxalic acid is manufactured for commercial purposes by heating sawdust with potassium or sodium hydroxide (KHO, NaHO.) with subsequent chemical treatments. The methods of securing calcium oxalate crystals were the following: On the patient entering the hospital a half a pint of urine was obtained, which was allowed to evaporate day by day in a warm room. By keeping a half a dozen bottles of urine

FIG. 4 (Byron Robinson) presents x-ray shadows of ureteral calculi (1-11). Number 11, about one-half size, I extirpated per vaginam. Nos. 22-45 are shadows of expelled urinary calculi; 25 and 28 are cystine calculi. Nos. 9 and 10 I extirpated from the uteretal pelvis and calyces by a lumbar incision. Nos. 34, 35, 36, and 40, calcium oxalate.

evaporating one can observe the various conditions of calcium oxalate crystals for comparison by mounting in glycerine. After the patient has been in the hospital a few days under visceral drainage, that is, under the administration of one-half pint of fluid every two hours for six times daily, the oxalate crystals are difficult to find. The diuresis has practically cleared the urine of crystals. The oxalate of calcium crystals may