278 PRACTICAL PHYSIOLOGY 



tion, ammonia till alkaline, and saturate the liquid with ammonium 

 sulphate crystals. A deep colour similar to that of permanganate 

 develops and reaches its maximum in fifteen minutes. This test 

 is more sensitive and distinctive than Legal's. 



lodoform Test. Distil a few c.c. of the urine with a few drops of 

 dilute sulphuric acid. To the distillate add a few drops of iodine 

 in potassium iodide solution and caustic soda till the iodine colour 

 disappears. lodoform is precipitated, and is detected by the 

 characteristic smell. 



EXPERIMENT XI. Test for Aceto-acetic Acid. To the urine add 

 ferric chloride solution in excess of that required to precipitate the 

 phosphate present. A deep red colour in the solution indicates the 

 presence of aceto-acetic acid. (Carbolic and salicylic acids in the 

 urine give a very similar colour.) 



/OH 



Homogentisic Acid is di-oxyphenyl-acetic acid C 6 H 2 ^ OH It 



\CH 2 COOH. 



reduces Fehling's solution. 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 can be easily separated from the urine by 

 adding a solution of lead acetate, filtering off the precipitate of inorganic salts 

 which at first forms and allowing the filtrate to stand, when large needle- 

 shaped glancing crystals of the lead salt separate out. If these be collected 

 and treated with sulphuretted hydrogen, so as to remove the lead, the acid is 

 obtained in a pure state. 



Glycuronic Acid. Chemically this is dextrose in which the end CH 2 OH 

 group has become oxidised to form COOH, or carboxyl. It has, accordingly, 

 the formula COOH (CH . OH) 4 CHO. It is an intermediate body in the 

 metabolism of dextrose, and usually becomes further decomposed in the 

 organism, to yield carbon dioxide and water. Sometimes, however, it unites 

 with the aromatic bodies (phenol, scatol, etc.) absorbed from the intestine 

 to form a salt. In this combination it takes the place of sulphuric acid (see 

 p. 264). In very small amount, it seems to be always present in the urine, 

 but under certain conditions (as after the administration of certain drugs) 

 it becomes increased to such an extent as to impart to the urine a very con- 

 siderable power of reducing metallic oxides in alkaline solution. When this 

 is the case it is apt to be confused with dextrose. The only absolute test 

 whereby it may be distinguished from dextrose is that it does not ferment 

 with yeast. It gives the pentose reactions. 



Lactic Acid, see p. 294. 



