380 CALCIFICATION, CONCRETIONS, AND INCRUSTATIONS 



compound of bilirubin ; and also Naunyn found that the bile 

 salts prevent precipitation of calcium- bilirubin, even when 

 calcium salts are added in considerable amounts. Apparently 

 it is the presence of proteid substances that leads to the precipi- 

 tation of this compound from bile, and hence the formation of 

 pigment calculi is also favored or initiated by inflammation of 

 the bile tracts, particularly as most of the calcium salts seem to 

 come from the mucous membrane ; l later, as we have seen, 

 these pigment concretions often become covered with cholesterin 

 derived from the injured epithelium, and the common mixed 

 calculi are then formed. In view of the fact that much of the 

 pigment in these calculi is composed of the oxidation products 

 of bilirubin, especially bttihumin, it is possible that oxidation 

 processes in the stagnating bile are important causes of the 

 precipitation ; Naunyn suggests that bacteria may be the cause 

 of the oxidation. Pigment calculi are particularly important 

 as the starting-point of the larger mixed calculi. It is possible, 

 Naunyn believes, for the pigment to be later gradually replaced 

 by cholesterin. 



URINARY CALCULI ' 



These differ from the bile concretions in two important re- 

 spects : first, their constituents are derived from the secretion 

 of the kidney rather than from the walls of the excretory pas- 

 sages, and they are usually deposited on account of an over- 

 saturation of the urine, or on account of a change in compo- 

 sition 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, 

 Finsterer found but six concretions composed of only one sub- 

 stance, 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 must be present as well as a binding 

 substance, which is often mucus derived from the walls of the 



1 Baldwin (quoted by Herter, loc. cit.) found human cystic bile to contain 

 an average of 0.072 per cent, of calcium, the amount not showing any constant 

 relation to the quantity of cholesterin present. The presence of calcium pig- 

 ment stones was not associated with an excess of calcium in the bile. 



2 General bibliography given by Finsterer, Deut. Zeit. klin. Chir., 1906 

 (80), 414. 



