UliATKS. OXALATE. MUCIN. 169 



is ordinarily hindered in urine by the presence of phos- 

 phates, chlorides and pigments. The conditions which 

 accelerate the change, the converse retarding, are (1) 

 acidity, (2) poverty of mineral salts, (3) little pigment, 

 (4) a high percentage of uric acid. 



Demonstration of Quadpiurates. Place a slight scraping of 

 serpent's excrement upon a glass slip, press it into a fine 

 powder with the blade of a knife and shake off all that 

 does not adhere to the glass. Cover dry and examine under 

 a power of 300 diams., observe the small globular masses 

 of quadriurate of ammonia which alone are present. Let 

 water flow between the glasses and recognise the almost 

 instantaneous appearance of a crop of short square-ended 

 needles of uric acid, which grow into fine parallel sided 

 colourless crystals or thin fusiform plates. Ammonium 

 urate remains as granules. 

 Acid Urates are far more soluble (at least 10 times) 



than uric acid ; nevertheless, they are the commonest pps in 



urine. 



Their deposition is favoured by (1) an acid reaction, (2) low 



temperature, (3) little water, (4) ammonium urate occurs in 



alkaline urine. 



A pp of urates in urine is coloured fawn to brick dust red, 



depending upon the quantity of pigment involved (uroerythrin). 

 These pps dissolve on heating, and so differ from phosphates 



which require an acid. 



Oxalate of Lime. 1 g in 24 hours. Is kept in solution in 

 the urine by acid sodium phosphate. 



It appears as a sediment after eating rhubarb, cabbage, &c., 

 as crystals which are regular octohedra, brilliant, and colourless. 



Mucin. Normally present in small quantity, collects on 

 standing as a faint cloud at the bottom of the vessel. 



