616 THE CHEMISTRY OE THE URINE. 
acid. They are found in the distillate so obtained, together with traces of 
hydrochloric and benzoic acids, phenol, and acetone. 
Sarcolactic acid is not a normal component of human urine, but it appears 
in many diseased or abnormal conditions of the body, of which it may be said 
generally that they involve either a suspension of normal hepatic functions or 
interference with the proper oxidative processes of the body. 1 It was first 
observed in the urine of phosphorus poisoning, and of acute yellow hepatic 
atrophy,- and may he always demonstrated in these conditions. It is found 
also after slow asphyxia ; in poisoning by carbon monoxide, in prolonged 
anaemia, and shortly before death in very many diseases. That it may appear 
after prolonged and severe exercise, is doubtless explained by the fact that 
oxidation in the body has not kept pace with the increased production of 
lactates in the muscles'. 3 
The three closely related substances, /3-hydroxybutyric acid, acetacetic 
acid (diacetic), and acetone rise to importance only in diabetes, but small 
quantities of the last may be found in normal urine, and all may be increased 
in disease apart from glycosuria. The following equations show the relation 
which obtains between them : 4 — 
CH 3 CH(OH).CHo.COOH + = CH 3 .CO— CH,.COOH + H,0 
()3-hydroxybutyric acid) (diacetic acid) 
CH3.CO— CH,.COOH = CH3.CO.CH, + C0 2 
(diacetic acid) (acetone) 
The first only appears in the urine in conjunction with the others, but 
either of the two latter may lie found alone. Large amounts of all three may 
be found in diabetes; of the hydroxy-acid many grammes may be passed in 
the day. 
The presence of diacetic acid may he demonstrated by making the urine 
acid with sulphuric acid, and shaking with ether ; the latter, which extracts 
the substance, is then transferred to another vessel, and is shaken with a weak 
aqueous solution of ferric chloride, which, if acetacetic acid was present in the 
urine, becomes of deep burgundy wine colour. 
In testing for the hydroxybutyric acid, advantage is taken of the fact that 
it yields a volatile derivative, a crotonic acid, on distilling with sulphuric acid. 
This substance crystallises out from the distillate of the urine, and may be 
identified by its melting point (72° C). The urinary hydroxybutyric acid is 
laevorotatory. 
Acetone is identified in a urinary distillate by first adding a few drops of a 
solution of sodium nitroprusside, and then caustic alkali, whereupon, in the 
presence of acetone, a fine cherry-red colour is produced. Acetic acid subse- 
quently added in excess changes the colour to purple (LegaVs t>-.<t). 
The Colour of Urine and the Chemistry of the Pigments. 
It is a familiar fact that, under physiological conditions, the urine 
may be almost colourless, or may exhibit tints varying from a pale 
straw yellow, through deep orange, to reddish brown. In its commonest 
condition it is yellow. Pathologically, the colour may undergo variations 
wider than those seen in health. 
1 Cf. Araki, Ztschr. f. physiol. C'hcm., Strassburg, 1895, Bd. xix. S. 422, with reference 
to previous papers by this author. 
2 Schultzen u. Riess, Chem. Centr.-BL, Leipzig, 1869, S. 6S1. 
3 Colasanti and Moscatelli, Arch. f. cxpcr. Path. u. Pltarmakol., Leipzig, 1890, Bd. 
xxvii. S. 158. 
4 Cf. Minkowski, ibid., 1893, Bd. xxxi. S. 183. 
