URINE 455 



low an interval of five hours may elapse before the color appears. 

 The test is believed to be specific for acetoacetic acid. 



H OHH 



I I I 



0-HYDROXYBUTYRIC ACID, H C C C COOH. 



I I I 



H H H 



This acid occurs in normal urine in traces, e.g., 2030 mg. per day. 1 

 It is found under certain pathological conditions in larger quantities 

 and then always in conjunction with either acetone or acetoacetic 

 acid. It is present in especially large amount in severe cases 

 of diabetes and has also been detected in digestive disturbances, 

 continued fevers, scurvy, measles, and in fasting. It is probable 

 that, in man, jS-hydroxybutyric acid, in common with acetone and 

 acetoacetic acid, arises principally from the breaking down of fatty 

 tissues within the organism. Any condition in which large amounts 

 of acetone and acetoacetic acid, and in severe cases ]8-hydroxybutyric 

 acid also, are excreted in the urine is known as an "acidosis." In 

 diabetes the deranged metabolic conditions cause the production of 

 great quantities of these substances which lead to an acid intoxication 

 and ultimately to diabetic coma. In severe diabetes 50100 grams 

 or over per day may be excreted. In such conditions the /3-hy- 

 droxybutyric acid may constitute 60-80 per cent of the total acetone 

 bodies. In rare cases we may have an excretion of large amounts of 

 0-hydroxybutyric acid with a low acetone output. An acidosis may 

 also occur under certain physiological conditions (see Chapter XVII on 

 Acidosis and Chapter XXVIII on Metabolism). 



Ordinarily 0-hydroxybutyric acid is an odorless, transparent syrup 

 which is levorotatory and easily soluble in water, alcohol, and ether; 

 it may be obtained in crystalline form. 



EXPERIMENTS 



i. Black's Reaction. 2 Inasmuch as the urinary pigments as well as any 

 contained sugar or acetoacetic acid will interfere with the delicacy of this test 

 when applied to the urine directly, the following preliminary procedure is neces- 

 sary: Concentrate 10 c.c. of the urine under examination to one-third or one- 

 fourth of its original volume hi an evaporating dish at a gentle heat. Acidify 

 the residue with a few drops of concentrated hydrochloric acid, add sufficient 

 plaster of Paris to make a thick paste and allow the mixture to stand until it 

 begins to "set." It should now be stirred and broken up hi the dish by means 

 of a stirring rod with a blunt end. Extract the porous meal thus produced twice 



1 Shaffer and Marriott: Jour. Biol. Chem., i<5, 265, 1913. 



2 Black: Jour. Biol. Chem.. 5, 207, 1908. 



