URINE 435 



sulphur sinks to the bottom of the liquid, the rapidity with which the sulphur sinks 

 depending upon the amount of bile acids present in the urine. The test is said to 

 react with bile acids when the latter are present in the proportion i : 120,000. 

 Allen 1 has recently suggested the quantitative determination of bile acids by a 

 surface tension method. 



5. Neukomm's Modification of Pettenkofer's Test. To a few drops of urine 

 in an evaporating dish add a trace of a dilute sucrose solution and one or more drops 

 of dilute sulphuric acid. Evaporate on a water-bath and observe the development 

 of a violet color at the edge of the evaporating mixture. Discontinue the evapora- 

 tion as soon as the color is observed. 



6. Peptone Test (Oliver). To 5 c.c. of urine add 2-3 drops of acetic acid, 

 filtering if necessary. Add an equal volume of a i per cent, solution of Witte's 

 peptone to the acid solution. A precipitate is formed which is insoluble in an excess 

 of acetic acid. This precipitate is a compound of protein and bile acids. 



CH 3 



I 



ACETONE, C=O. 



CH 3 



It was formerly very generally believed that acetone appeared in the 

 urine under pathological conditions because of increased protein de- 

 composition. It is now generally thought that, in man, the output 

 of acetone arises principally from the breaking down of fatty tissues 

 or fatty foods within the organism. The quantity of acetone elimi- 

 nated has been shown to increase when the subject is fed an abundance 

 of fat-containing food as well as during fasting, whereas a replace- 

 ment of the fat with carbohydrates is followed by a marked decrease 

 in the acetone excretion. If no carbohydrate food is fed the output of 

 acetone bodies increases at once, producing a physiological acidosis 

 (see Chapter XXVII on Metabolism). 



Acetone and the closely related bodies, /3-hydroxybutyric acid and 

 acetoacetic acid, are generally classified as the acetone bodies. They 

 are all associated with a deranged metabolic function and may appear 

 in the urine together or separately, depending upon the conditions. 

 Acetone and diacetic acid may occur alone in the urine but /3-hy- 

 droxybutyric acid is never found except in conjunction with one or the 

 other of these bodies. Acetone and acetoacetic acid arise chiefly 

 from the oxidation of /3-hydroxybutyric acid. The relation existing 

 between these three bodies is shown in the following equations. 



(a) CH3.CH(OH).CH2.COOH+0-^CH 3 CO.CH 2 .COOH+H20. 



0-Jiyd.roxybutyric acid. Acetoacetic acid. 



(b) CH 3 CO.CH2.COOH->(CH 3 )2CO+C02. 



Acetoacetic acid. Acetone. 



1 Allen: Jour. Biol. Chem., 22, 505, 1915. 



