294 URINE. [CH. XII. 



Uric acid occurs to the extent of about 0-7 gram, in the 

 24 hours' urine, but the amount excreted varies with the 

 diet and the individual. 



From its close chemical relationship to the purine 

 bases formed by the hydrolysis of the nucleins of the food 

 and tissues (see p. 63), the view is commonly held that 

 uric acid has its origin in the cellular organs of the body 

 from the oxidation of such substances. Thus we can have 

 uric acid arising exogenously from the free or combined 

 purines of the food and also endogenously from those of 

 the tissues. This view is apparently supported by the 

 fact that the administration of foods rich in nucleoproteins, 

 as sweetbreads, or of certain of the pure purine bases, 

 does cause an increased excretion of uric acid. 



It is possible that a certain proportion of the uric acid 

 formed in the body is destroyed by the liver, so that the 

 amount excreted is a balance between that formed and that 

 destroyed. 



In gout, in which there is a deposition of uric acid in 

 the tissues, the excretion is decreased before an acute 

 attack, is increased during the attack, and then falls again. 

 In this condition there is a recognisable amount of uric 

 acid in the blood (see above). For the method of estima- 

 tion in urine see Ex. 406. 



348. Treat a small amount of uric acid with 10 cc. of 2 per 

 cent, sodium carbonate. Heat nearly to boiling and cool. Note 

 that a considerable portion of the uric acid has dissolved in the form 

 of a urate. 



349. Filter the solution and treat a portion with a drop or two 

 of strong hydrochloric acid and shake. A white crystalline pre- 

 cipitate of uric acid separates out, showing that uric acid is very 

 insoluble in water. Allow the crystals to settle, remove a few by 

 means of a pipette, and examine them microscopically. They 

 usually form rhombic plates. Draw the crystals. 



NOTE. If the solution is very strong, the uric acid may separate out in an 

 amorphous form. Should this be the case, make the solution alkaline and heat 

 to dissolve. Whilst still hot add some I1C1 and allow the tube to cool slowly. 



