THE COMPOSITION AND CHARACTERS OF THE URINE 1173 



protein in its diet, these substances will leave the body conjugated, not with sulphuric 

 acid, but with glycuronic acid. Glycuronic acid may be regarded as the first product 

 of oxidation of glucose, having the formula : 



COOH 



I 

 (CHOH) 4 



CHO 



It reduces Fehling's solution and rotates the plane of polarised light to the left. 



OXY-FATTY ACIDS AND ACETONE. These substances occur often associated 

 with glucose in diabetes, especially towards the end of the disease. They represent the 

 penultimate stages in the oxidation of the fats. Their relation to one another is seen 

 from their formulae : 



CH 3 CH 3 CH 3 



CHOH CO CO 



I I I 



CH 2 CH 2 CH 3 



COOH COOH 



Oxybutyric acid Aceto-acetic acid Acetone 



They may also occur in any condition of carbohydrate starvation, relative or absolute. 

 Thus they are found in the urine during absolute starvation as well as in individuals 

 on a pure fat and protein diet. The two acids are generally found associated in the 

 urine. 



The presence of aceto- acetic acid may be detected as follows : 



(1) To some urine add ferric chloride as long as a precipitate of ferric phosphate con- 

 tinues to form. Filter this off and to the filtrate add a few more drops of ferric chloride. 

 If the acid be present a claret colour is produced. 



(2) On heating with dilute alkali, aceto-acetic acid is decomposed, with the pro- 

 duction of acetone. This may be detected by its odour or by distilling off a small 

 proportion of the fluid and testing the distillate -in the following ways : 



(a) On the addition of sodium hydrate and iodine and warming, iodoform is formed. 



(6) Legal's test. A few drops of freshly prepared sodium nitroprusside solution is 

 added and the mixture rendered alkaline with sodium hydrate. A deep red colour is 

 formed. On acidifying with acetic acid this colour is changed to a reddish purple. 



CYSTINE. This substance, which is a normal product of the hydrolysis of proteins, 

 is found as a constant constituent to the amount of half a gramme a day in the urine of 

 certain individuals. The condition of cystinuria represents, like alcaptonuria, an inborn 

 error of metabolism. It is found in the child and persists throughout life. In such 

 cases the cystine may give rise to urinary deposits or even to a urinary calculus. 



HOMOGENTISIC ACID. This is an aromatic acid having the composition of 

 dioxyphenyl' acetic acid. Its formula is as follows : 



OH 



I CH 2 .COOH 



OH 



It occurs as a constituent of the urine of certain individuals, who are said to be 

 affected with alcaptonuria. The urine of these cases is remarkable for its resistance to 

 putrefactive changes. It slowly darkens on exposure to the air, and on the addition of 

 alkali and shaking with air it becomes rapidly brown or black. It reduces Fehling's 

 solution, so that the presence of sugar may be suspected. Such urine contains homogen- 



