278 PEACTICAL PHYSIOLOGY 



colours is then very distinct. Also apply Matthew Hay's test (see 

 p. 233). 



Acetone in the Urine. In severe diabetes this body occurs in the 

 urine. It is also present in the urine in experimental diabetes, when 

 this is accompanied by the breaking down of proteid tissues. As 

 intermediate bodies aceto-acetic acid and /3-oxybutyric acid are formed. 

 The relationship between these three bodies will be seen from the 

 following equations : 



(1) /3-oxybutyric acid = CH 



(2) Aceto-acetic acid CH 3 CO 



(3) Acetone CH 3 CO CH 3 . 



/3-oxybutyric acid is the first formed and soon becomes oxidised to 

 form aceto-acetic acid, which then splits into acetone and carbonic acid. 

 There are simple tests for aceto-acetic acid and acetone ; /3-oxybutyric 

 acid, for which there is no simple test, always occurs along with aceto- 

 acetic acid. 



EXPERIMENT XL Test for Aceto-acetic Acid. Add to the urine 

 dilute ferric chloride, allow the precipitated ferric phosphate to settle. 

 The supernatant fluid becomes red if aceto-acetic acid be present. 



EXPERIMENT XII. Test for Acetone. The urine has a peculiar 

 fruity odour. Add a few drops of caustic potash, warm and add, drop 

 by drop, a saturated solution of iodine in potassium iodide till a brown 

 colour is produced. Now add more caustic potash and boil ; a smell of 

 iodoform is given off. 



There are numerous other bodies which may occur in the urine in 

 disease, and their description will be found in text-books on clinical 

 medicine. There are two of these, however glycuronic acid and 

 homogentisic acid which are of great physiological interest, first of 

 all, because they both have the power of reducing metallic oxides in 

 alkaline solution, and may, accordingly, be confused with dextrose; 

 and secondly, because they both indicate an unusual form of meta- 



bolism. 



/OH 

 Homogentisic Acid is di-oxyphenyl-acetic acid C 6 H 3 ^-OH 



\CH 2 COOH 



When present in the urine it causes the latter to become of a dark- 

 brown colour on standing, or this change in colour may be hastened by 

 adding some alkali. It is present in the urine during the whole life, 

 and it has been noticed that persons who exhibit it are almost invari- 

 ably the children of first cousins. It can be easily separated from the 

 urine by adding a solution of lead acetate, filtering off the precipitate 



