THE URINE. 431 



a formation takes place, for instance, when a foreign body in the 

 bladder produces catarrh accompanied by alkaline fermentation. 



We discriminate between the nucleus or nuclei if such can be 

 seen and the different layers of the calculus. The nucleus may 

 be essentially different in different cases, for quite frequently it 

 consists of a foreign body introduced into the bladder. The calcu- 

 lus may have more than one nucleus. In a tabulation made by 

 ULTZMAN^ of 545 cases of urinary calculi, the nucleus consisted in 

 80.9$ of the cases, of uric acid (and urates); in 5.6$, of calcium 

 oxalate; in 8. 6$, of earthy phosphates ; in 1.4$, of cystin; and in 

 3.3$, of some foreign body. 



During the growth of a calculus it often happens that, for some 

 reason or other, the original calculus-forming substance is covered 

 with another layer of a different substance. A new layer of the 

 original substance may deposit on the outside of this, and this pro- 

 cess may be repeated. In this way a calculus consisting originally 

 of a simple stone may be converted into a so-called compound stone 

 with several layers of different substances. Such calculi are always 

 formed when a primary formation is changed into a secondary. By 

 the continued action of an alkaline urine containing pus, the prim- 

 ary constituents of an originally primary calculus may be partly 

 dissolved and be replaced by phosphates. Metamorphosed urinary 

 calculi are formed in this way. 



Uric-acid calculi are very abundant. They are variable in size 

 and form. The size of the bladder-stone varies from that of a pea 

 or bean to that of a goose-egg. Uric-acid stones are always colored ; 

 generally they are grayish yellow, yellowish brown, or pale red- 

 brown. The upper surface is sometimes entirely even or smooth, 

 sometimes rough or uneven. Next to the oxalate calculus, the uric- 

 acid calculus is the hardest. The fractured surface shows regular 

 concentric, unequally-colored layers which may often be removed 

 as shells. These calculi are formed primarily. Layers of uric-acid 

 sometimes alternate with other layers of primary formation, most 

 frequently with layers of calcium oxalate. The simple uric-acid 

 calculus leaves very little residue when burnt on a platinum foil. 

 It gives the murexid test, but there is no mentionable development 

 of ammonia when acted on by caustic soda. 



Ammonium-urate calculi occur as primary calculi in new-born 



