384 CALCIFICATION, CONCRETIONS, AND INCRUSTATIONS 



Cystin calculi are rare but very interesting formations. 

 ^ . S-CH(NH 2 )-COOH . 

 Cystm | is important as the sulphur-containing 



S-CH(NH 2 )-COOH 



portion of the proteid molecule. Under normal conditions all 

 the cystin taken in food is completely oxidized and none (or 

 uncertain traces) appears in the urine. In certain individuals 

 the urine contains considerable quantities of cystin constantly 

 (cystinuria, see Chap, xix), and occasionally in these cases soft 

 concretions of nearly pure cystin are formed in the urinary 

 passages. Cystiu calculi may reach the size of a hen's egg, are 

 crystalline in structure, and in the urine of such patients the 

 characteristic hexagonal crystals may usually be found. Loewy 

 and Neuberg 1 have contended that the cystin found in urinary 

 calculi is an isomer of the cystin found in the proteid molecule, 

 and that cystinuric patients can completely oxidize proteid 

 cystin, but not the stone cystin. This claim has not been sub- 

 stantiated, however. 2 



Xanthin Calculi. Xanthin is the most abundant of the 

 purin' bases normally present in urine, but the total amount is 

 extremely small. Like uric acid, it fluctuates in amount 

 according to the amount of destruction of nucleoproteids, either 

 of the food or of the tissues. Concretions consisting chiefly 

 of xanthin, which is often mixed with uric acid, are extremely 

 rare, but a few isolated specimens having been described. 



Indigo calculi, derived from the indican of the urine 

 through oxidation, have also been described a few times. 



Urostealith calculi, composed of fatty matter, have been 

 occasionally observed. Although some of the concretions des- 

 cribed under this head have really represented foreign bodies 

 introduced through the urethra (e. g., Kruckenberg's concretion 

 of paraffin from a bougie), yet true fat concretions do occur. 

 The origin of the fat in these stealiths is unknown, possibly 

 it comes from degenerated epithelium. Horbaczewski 3 analyzed 

 such a specimen which had the following percentage composition : 



Water 2.5 



Inorganic matter 0.8 



Organic matter (chiefly proteid) . . 11.7 



Fatty acids 5.1.5 



Neutral fat 33.5 



Cholesterin traces 



1 Zeit. physiol. Chem., 1904 (43), 338. 



2 Rothera, Jour, of Physiol., 1905 (32), 175. Literature concerning cystin, 

 see Friedmann. Ergeb. der Physiol., 1902 (i), 15; Marriott and Wolf, Am. 

 Jour. Med. Sci.', 1906 (131), 197. 



3 Zeit. physiol. Chem., 1894 (18), 335. 



