452 PRACTICAL PHYSIOLOGY 



Normal human urine has an average reducing power equivalent to 

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

 is due to dextrose, 8 per cent, to uric acid (see p. 425), and 25 per 

 cent, to creatinin (see p. 429), 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 



When great accuracy is required, in order to remove all the urochrome as 

 well as a considerable proportion (75 per cent.) of the uric acid and creatinin, 

 Bang and Bohmannsson use blood charcoal and hydrochloric acid. We have 

 obtained more constant results, however, by using acetone 1 and blood charcoal 

 according to the following method : 



20 c.c. urine are mixed in a flask with 5 c.c. acetone and 2 gr. charcoal 

 from blood (a teaspoonful). The flask is then shaken occasionally during five 

 minutes, after which its contents are filtered through a dry filter paper into 

 a test tube. Of the filtrate (which is always perfectly colourless) 5 c.c. 2 are 

 used for Bang's titration, as described on page 293. 



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

 reduces but does not ferment with yeast ; it gives Bial's test (p. 295). 

 The presence of laevulose is revealed by Seliwanoff's test (p. 278). 



The Acetone Bodies in Urine. These substances are: 



(1) /3-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 /3-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 therefore 

 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 



1 The acetone must be chemically pure, otherwise it may contain reducing 

 substance. 



2 This amount of the filtrate is for a urine containing not more than 2 per 

 cent, dextrose. If it contain less than 0*5 per cent, dextrose 10 c.c. of the 

 filtrate should be taken. If it contain more than 2 per cent. 2-3 c.c. When, 

 however, more than 2 or 3 per cent, dextrose is present the polariscopic method, 

 or Bang's titration, without the addition of charcoal, will probably give close 

 enough results for most purposes. 



