616 THE CHEMISTRY OP 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, 2 and may be 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).CH 2 .COOH + - CH 8 .CO CH 2 .COOH + H 2 



(/3-hydroxybutyric acid) (diacetic acid) 



CH 3 .CO CH 2 .COOH - CH 3 .CO.CH 3 + C0 2 



(diacetic acid) (acetone) 



The first only appears in the urine in conjunction with the others, but 

 either of the two latter may be 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 be 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 hydroxy butyric 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 hydroxy butyric 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 (Legal's test). 



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. Chem., Strassburg, 1895, Bd. xix. S. 422, with reference 

 to previous papers by this author. 



2 Schultzenu. Riess, Chem. Centr.-BL, Leipzig, 1869, S. 681. 



3 Colasanti and Moscatelli, Arch. f. exper. Path. u. PharmdkoL, Leipzig, 1890, Bd. 

 xxvii. S. 158. 



4 Cf. Miukowski, ibid., 1893, Bd. xxxi. S. 183. 



