568 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



3. URINARY CALCULI. 



The various constituents of urine which form sediments may take part in 

 the formation of urinary calculi, which are of frequent occurrence and vary in 

 size from that of a pea to that of a goose egg. They are generally coloured, 

 commonly yellow-grey, yellow-brown or reddish-brown. Their surface may 

 be smooth and polished, or rough and uneven. When fractured, they ap- 

 pear to consist of regular concentric layers which can often be scaled off. 



(1) Urate Stones. 



They consist generally of ammonium urate and are of a brown colour and 

 very hard ; they are pale yellow when powdered. They give the murexide 

 reaction and ammonia is evolved on boiling with caustic soda. 



(2) Calcium Oxalate Stones. 



After the urate stones these are the most frequent in occurrence. They 

 are either smooth and small, " hempseed stones," or as large as a hen's egg 

 with a rough and uneven surface, " mulberry stones ". They cause haemor- 

 rhage and have therefore a superficial dark brown colour. They are soluble 

 in hydrochloric acid without effervescence, but not in acetic acid. On heating 

 they are converted into calcium carbonate, which dissolves in acetic acid 

 with effervescence. 



(3) Phosphate Stones. 



These stones can reach a large size. They consist of calcium phosphate 

 and triple phosphate and generally contain ammonium urate and calcium 

 oxalate. Their colour varies : it may be white, grey, pale yellow, or even 

 lilac (from indigo red). Their surface is uneven. They do not burn on 

 heating ; when crushed the powder is soluble in acids without effervescence 

 and the solution gives the reactions for phosphoric acid and calcium. Am- 

 monia is evolved from stones containing triple phosphate on heating with 

 caustic soda. 



(4) Calcium Carbonate Stones. 



These stones occur chiefly in herbivora and very rarely in man. They 

 have a chalky appearance, are white in colour and dissolve in acids with evolu- 

 tion of carbon dioxide. 



(5) Cystine Stones. 



These stones are rare and of various sizes. They may be as large as a 

 hen's egg. Their surface is smooth or uneven, white or dull yellow, and 

 they show a crystalline fracture ; they are not very hard. On heating they 

 burn away almost entirely with a blue flame. They give the reaction for 

 cystine (p. 144). 



(6) Xanthine Stones. 



These stones are still rarer and vary in size from a pea to a hen's egg. In 

 colour they are dull white, yellow-brown or red-brown. They are not very 

 hard and they show an amorphous fracture, becoming waxy on rubbing. 

 They are completely combustible and give a yellow murexide reaction. 



(7) Urostealiths. 



These stones have only been observed a few times. They are soft and 

 elastic when wet, brittle, amorphous and waxy when dry. They burn with a 

 luminous flame when heated and consist of fat and cholesterol. 



