376 CALCIFICATION, CONCRETIONS, AND INCRUSTATIONS 



structure. Frequently both of these lines of formation are 

 easily discerned, but either one or the other may become 

 obscured. 



The chemistry of concretions is, therefore, a relatively simple 

 matter, and it remains merely to give the chief facts concerning 

 the formation and composition of the different varieties. 



BILIARY CALCULI 



As may be judged from the above statements, concretions are 

 never composed of one substance in a pure form, but usually con- 

 sist of a mixture of the constituents of the fluid in which they 

 are developed. This is particularly true of gall-stones, which 

 contain in greater or less quantities several or all of the constitu- 

 ents of the bile. While cholesterin forms the greater part of 

 nearly all biliary concretions, and is present in greater or less 

 amounts in all, calcium salts of the bile-pigments are always 

 present ; usually inorganic salts of calcium (carbonate and phos- 

 phate) are also present, as well as small amounts of fats, soaps, 

 lecithin, mucus, and other products, and occasionally traces of 

 copper, iron, and manganese. 1 The quantity of bile salts, the 

 chief constituent of the bile, is usually extremely minute, appar- 

 ently only so much as may percolate into the crevices of the 

 concretion. However many stones there may be in a gall- 

 bladder, they usually are all of approximately the same com- 

 position and structure. 



In gall-stones from the domestic animals the proportion of 

 inorganic salts is usually much higher than it is in man. 



Naunyn has classified gall-stones according to their composi- 

 tion, as follows : 



1. " Pure" Cholesterin 2 Stones. The purity is only rela- 

 tive, since even the purest always contain some pigment as well 

 as a stroma and a nucleus ; but the amount of cholesterin may 

 reach 98 per cent., and is usually over 90 per cent. Crys- 

 talline structure is usually well marked, while stratification is 

 slight. The color varies from nearly pure white to yellow, or 

 even brown on the surface. 



2. Laminated Cholesterin Stones. These consist of about 

 75-90 per cent, of cholesterin, and differ from the preceding 

 form in containing more pigment, which is deposited in layers 

 alternating with the white layers of cholesterin. The pigment 



^all-stones have been found enclosing droplets of mercury. (Naunyn, 

 Frerichs.) 



2 Concerning composition and occurrence of cholesterin, see pages 28 and 

 346. 



