6 1 4 THE CHEMISTRY OF THE URINE. 
glucuronic 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) 1 
is often found in the urine, and analogous compounds arise after the 
administration of butylchloral hydrate and chloroform. 
All these compounds are hevorotatory, 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 ; some (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 ('(impounds, a largo 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 on", 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), are present 
in all specimens of urine, about 50 ingrms. 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:" 1 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. dev.tsch. ch&m. Gesellsch., Berlin, 1875, Bd. viii. S. 662. 
2 Cf. Ashdown, Brit. Med. Joum., London, 1890, vol. i. p. 169. 
3 Gaglio, Arch. f. exper. Path. v. Pharmakol., Leipzig, 1SS7, Bd. xxii. S. 246. 
4 Marfori, Jahresb. ii. d. Fortschr. d. Thicr-Chcm., Wiesbaden, 1S92, S. 72. 
