ELEMENTARY CHEMICAL PHYSIOLOGY 



277 



Calculation. 5 divided by volume of sugar solution used = per 

 cent, sugar. 



Amount of sugar which reduces 



Normal human urine has an average reducing power equivalent to 

 about 0-2 per cent, dextrose. Of this reducing power about 18 per 

 cent, is due to dextrose, 8 per cent, to uric acid (see p. 259), and 

 25 per cent, to creatinine (see p. 261), the remaining 50 per cent, 

 being probably due to urochrome. Furthermore, the colour of 

 urine renders the end-point of the titration much more uncertain 

 than when a watery solution of dextrose is employed. 



Sometimes the urine contains pentose (i-arabinose). In such cases 

 it reduces but does not ferment with yeast ; it gives Tollen's test 

 (p. 326). 



The presence of Icevulose is revealed by SeliwanofTs test (p. 210). 

 It must not be forgotten that many urines give a definite red colour 

 on heating with concentrated hydrochloric acid alone. 



The Acetone Bodies in Urine. These substances are : 



(1) ^-oxybutyric acid, CH 3 . CHOH . CH 2 . COOH. 



(2) Aceto-acetic acid, CH 3 . CO . CH 2 . COOH. 



(3) Acetone, CH 3 . CO . CH 3 . 



Aceto-acetic acid is an oxidation product of /?-oxybutyric acid. 

 Acetone is formed from aceto- acetic acid by the loss of carbon 

 dioxide. A solution of aceto-acetic acid partially decomposes to 

 acetone at ordinary temperatures. On boiling the decomposition 

 becomes complete. 



Acetone is present in minute traces in normal urine. All three 

 bodies make their appearance in human urine when fat is being 

 metabolised at an unusually rapid rate. They are present there- 

 fore in the urine of severe cases of diabetes, in the urine of starvation, 

 and in the urine of many people when the carbohydrate of the diet 

 is reduced below 70 gms. per diem. Under these conditions the 

 amount of the acetone bodies is increased by exercise. 



EXPERIMENT X. Tests for Acetone. Legal's Test. Add to the 

 urine in a test tube a few drops of a fresh solution of sodium 

 nitroprusside and then caustic soda solution till definitely alkaline. 

 A permanent red colour develops, which becomes deeper and assumes 

 a purplish tint on acidifying with strong acetic acid. (Compare 

 with test for creatinine.) 



Rothera's Test. Add a few drops of sodium nitroprusside solu- 



