THE URINE 461 



fluid. It is obtained on oxidation of uric acid by a ferment uricase 

 or by oxidising agents (ozone, permanganate of potash). 



HN--CO 



oc c 



I 



HN C NH NH 



It can be synthesized out of glyoxylic acid (COOH.CHO) and urea, and 

 is a diureid of glyoxylic acid. 



Creatinin (C 4 H 7 N 3 O) is excreted in the urine in such a very constant 

 amount about 1 gramme in twenty-four hours that some have 

 regarded it as a measure of the nitrogenous metabolism of the tissues 

 (endogenous metabolism). Creatin, or methylguanidin-acetic acid 

 is found in the muscles, and therefore in meat extracts. On 

 heating with dilute H 2 S0 4 , it passes into its anhydride, creatinin. 

 Creatin is excreted when the protein substance of the bod}- is being 

 broken down, and occurs in the urine during starvation and fevers, 

 also during lactation. The creatin which is eaten in meat is probably 

 decomposed by the intestinal bacteria. 



The relationship of the creatin to the creatinin of the body is a 

 matter of considerable complexity. Contrary to what was once 

 believed, it is probable that creatinin is the mother-substance of 

 creatin, and not creatin of creatinin. It is possible that creatinin 

 is formed in the liver from some product of protein digestion, and 

 that the creatin of the muscles is built up from the creatinin thus 

 formed. 



The presence of creatinin in the urine is shown by adding a few 

 drops of a saturated solution of picric acid and a little 20 per cent, 

 solution of caustic potash. A transparent red colour is jproduced 

 (Jaffe's test). Sugar in the urine gives the same colour, but deeper 

 and opaque. Thus, there is no difficulty in distinguishing between 

 the two. 



Another test for creatinin is to add a few drops of a freshly pre- 

 pared solution of sodium nitroprusside and 20 per cent, solution of 

 caustic potash to the urine. A red colour is /^ 

 produced, which disappears on heating or on \j^ 

 the addition of acetic acid. />_ 



Oxalates occur in the urine combined with 

 calcium, and the salt is normally kept in solu- 

 tion by the acid sodium phosphate present. 

 When precipitated, it occurs as envelope or 



dumb-bell shaped crystals insoluble in acetic , 



i -i ill- i. j ui -j /-BV ni*A\ J' IG - 224. CALCIUM <)x- 

 and easily soluble in hydrochloric acid (Fig 224). A L A T E CRYSTALS. 



About OK)17 gramme of oxalic is excreted daily. (Savill.) 



This is mainly derived from the food, and is 



increased by the ingestion of fruits and vegetables, such as rhubarb, 



strawberries, tomatoes, spinach, cabbage. There are cases of " oxa- 



