6 1 4 THE CHEMISTRY OF THE URINE. 



glycuronic acid with members of the fatty group of alcohols, which are 

 excreted after the use of certain common drugs. Thus, when chloral 

 hydrate is being taken, trichlorethylglycuronic acid (urochloralic acid) l 

 is often found in the urine, and analogous compounds arise after the 

 administration of butylchloral hydrate and chloroform. 



All these compounds are leevorotatory, though glycuronic acid itself 

 is dextrorotatory ; many of them, urochloralic acid for instance, reduce 

 bismuth and copper solutions freely, and their presence may therefore 

 lead to error in testing for sugar ; but they are not fermentable. They 

 split up with varying degrees of ease into glycuronic acid and the 

 conjugated substance, either by boiling with mineral acids, or when 

 heated with water in sealed tubes ; ome (e.g. phenolglycuronic acid) 

 decompose when boiled with water alone. 



Glycuronic acid itself is a syrupy substance, soluble in water and 

 alcohol ; but when its aqueous solutions are boiled or evaporated, it 

 loses water, and forms a crystalline anhydride which is insoluble in 

 alcohol. 



To separate the urinary glycuronic compounds, a large quantity of urine is 

 precipitated with acetate of lead, and the precipitate decomposed with 

 sulphuretted hydrogen. After filtering, barium hydrate is added to the 

 solution. The sulphates and phosphates thus precipitated are filtered off, and 

 alcohol added to the filtrate, whereupon the barium salts of the conjugated 

 glycuronic acids crystallise out. 2 



OTHER ORGANIC COMPOUNDS. 



Oxalic acid. Small quantities of oxalic acid (COOH) 2 are present 

 in all specimens of urine, about 50 mgrms. being the average for the 

 day's excretion. Much of this may arise directly from preformed 

 oxalates ingested with the food, as all vegetable food contains traces of 

 these salts, and direct experiment has shown that they are susceptible 

 of but very incomplete oxidation in the body. 3 But oxalic acid does 

 not disappear from the urine when pure flesh-food is taken, nor even 

 during starvation; 4 it would thus seem certain that it can arise 

 from proteid metabolism. It is, in certain cases, very largely increased 

 in amount, from causes which are not clearly understood. Some 

 authorities hold that these cases of " oxaluria " depend always upon 

 excess of preformed oxalates in the diet ; but no one who has observed 

 the marked tendency to increased oxalate excretion in diabetes, or the 

 way in which, in some cases of glycosuria, a temporary decrease in the 

 sugar may be associated with an increase of oxalates, can doubt that it 

 may arise also from incomplete oxidation of carbohydrates. 



Oxalate of calcium frequently separates from the urine to form a 

 crystalline deposit. It mostly takes the form of the so-called 

 " envelope crystals," but may appear as dumb-bells, and is often seen as 

 clear o voids (Fig. 56). It is responsible for the formation of a variety of 

 urinary calculus. 



1 This was the first of these substances to be described, vide Musculus and v. Mering, 

 Ber. d. deutsch. chem. Gesellsch., Berlin, 1875, Bd. viii. S. 662. 



2 Of. Ashdown, Brit. Med. Journ., London, 1890, vol. i. p. 169. 



8 Gaglio, Arch. /. exper. Path. u. PIiarmaJcoL , Leipzig, 1887, Bd. xxii. S. 246. 

 4 Marfori, Jahresb. it. d. Fortschr. d. Thier-Chem., Wiesbaden, 1892, S. 72. 



