URINARY CONCRETIONS 459 



Urinary Calculi'* 



These differ from the bile concretions in two important respects: 

 First, there is no evidence that any considerable part of their con- 

 stituents may come from the walls of the cavities that contain them ; 

 they are usuall}^ deposited on account of an over-saturation of the 

 urine, or on account of a change in composition of the urine, which 

 renders them insoluble. Second, the composition of urinary calculi is 

 usually less mixed than that of biliary calculi, although seldom, if ever, 

 is it pure. Thus, Finstcrer found but six concretions composed of 

 onlj' one substance, in a collection of 114 calculi. As with the bile, the 

 chief constituent of the urine (urea) is so soluble that it never forms 

 concretions, but only the less soluble minor constituents are thrown 

 down. For the formation of calculi, however, it is not sufficient to 

 have merely an excess of a substance in the urine, for we may have 

 deposition of urates, phosphates, or uric acid in simple crystalline 

 form without the formation of calculi. A nucleus of some sort is 

 present as well as a binding suhsiance,^^ which is often mucus derived 

 from the walls of the passages, although the center of the concretion 

 most often consists of uric acid or urates. 



Although the amount of colloidal material in urine is relatively 

 small, yet it undoubtedly plays an important part in maintaining in 

 solution the less soluble crystalloids, which are especially the urates and 

 calcium oxalate. Normal urine contains no colloids which form irre- 

 versible gels, and hence ordinary deposits can be readily dissolved, but 

 in inflammatory conditions there appears fibrinogen which readily 

 forms the irreversible fibrin, and conditions thus become favorable for 

 the formation of concretions of any crystalloid with which the urine 

 may be saturated or over-saturated at the time (Schade). Possibly 

 other colloids may play a similar role. Aschoff and Kleinschmidt' 

 hold that most urinary calculi begin as primary calculi, formed inde- 

 pendent of inflammation from excess of the main constituent (uric acid, 

 oxalates, xanthine, but chiefly ammonium urate) ; this calculus forms 

 the crystalline nucleus of the laminated secondary deposits of other 

 substances, chiefly uric, acid, oxalates and phosphates, all being 

 deposited without inflammation. The inflammatory formations con- 

 sist chieflj'^ of ammonio-magnesium phosphate and ammonium urate, 

 usually deposited on a foreign body or a primarj^ calculus. The ex- 

 tensive study of the microscopic structure of urinary calculi by 

 Shattock,- shows also that a nucleus of cells or other organic material 

 is, at least in uric acid calculi, extremely rare, the center being almost 

 always a primary crystalline deposit from a supersaturated solution. 



"* General Bibliography given by Finsterer, Deut. Zeit. klin. Chir., 1906 (80), 

 41 -4; and Lichtwitz.'= 



^' Hippocrates appreciated the existence and importance of the mucoid binding 

 substance in urinary concretions (Schepelmann, Berl. klin. Woch., 1911 (48), 525). 

 ^"Die Harnsteine," Berlin, Julius Springer, 1911. 



2Proc. Roy. Soc. Med., Path. Sec, 1911 (4), 110. 



