URINE AND ITS CONSTITUENTS. 745 



Urinary calculi are solid deposits of various sizes formed from 

 the urine within the kidney, ureter, bladder, and urethra. They 

 may contain all the constituents of urine which occur as sediments, 

 and also certain pathological constituents deposited around an organic 

 framework. 



Calculi are cal led primary when formed in unchanged urine, and secondary 

 when they are formed in urine which has undergone decomposition. Uric 

 acid, calcium oxalate, calcium carbonate, xanthine, and cystic calculi are 

 primary formations, while ammonium urate, phosphatic and urostealith calculi 

 3,re secondary. 



During the development of a calculus the original deposit may be covered 

 by a layer of a different material, which in turn may be covered by another 

 substance. For this reason a simple stone may be converted into a compound 

 one. In this way a primary stone, by irritation of the bladder producing 

 cystitis, accompanied by alkaline fermentation, causes a deposition of phos- 

 phates, and is converted into a secondary calculus. The further action of the 

 alkaline urine may dissolve the primary calculus, replacing it with phosphates. 



In examining calculi it is necessary to make a section through the 

 centre of the calculus and scrape off a little from each layer, the 

 portions being examined separately. They may be found to be alike 

 (simple calculi) or unlike (compound or mixed calculi) in composi- 

 tion. The following scheme serves for a qualitative examination of 

 calculi. Heat some of the powdered calculus on platinum foil, when 

 the material will either burn and char without a flame (A), or burn 

 with a flame (B), or will not burn at all (C). (It should be remem- 

 bered that a calculus generally contains a little organic matter, so that 

 slight carbonization is always to be expected on heating it.) 



A. To the material burning without a distinct flame apply the 

 murexide test. If affirmative, uric acid or urates are indicated. 

 Heat some powder with potassium hydroxide; a strong odor of 

 ammonia proves the calculus to consist of ammonium urate; a nega- 

 tive result shows it to be uric acid. If the murexide test was nega- 

 tive, test for xanthine. The powder wall dissolve in nitric acid 

 without effervescence, leave on evaporation a yellow residue, turning 

 orange with alkali and red on heating. 



B. Material burning with a distinct flame may either be soluble 

 in alcohol and ether (urostealith) or insoluble in these solvents, but 

 soluble in potassium hydroxide solution on heating (fibrin), or soluble 

 both in hydrochloric acid and in caustic alkalies (cystine). Urostea- 

 lith burns with a yellow flame and emits the odor of burning resin. 

 Fibrin burns also with a yellow flame, but emits odor of burnt 

 feathers. Cystine burns with a pale-blue flame, emitting a peculiar 



