448 CALCIFICATIOX, COXVJi'KTWXS, AXD INCRUSTATIONS 



tiou depends upon two factors : The crystals tend to be deposited at 

 right angles to the surface, and thus give a radiating structure; but 

 the rate of deposition is usuall}^ irregular, and during the periods of 

 quiescence the surface tends to become covered witii mucin or other 

 organic substances, hence we also get a concentric, lami)iated struc- 

 ture. Frequently both of these lines of formation are easily dis- 

 cerned, but either one or the other may become obscured. 



Concretions consist, therefore, of mixtures of colloids and crystal- 

 loids deposited from solutions of the same character, and hence the 

 application of the principles of colloidal chemistry throws much 

 light on the conditions of their formation/''^ Colloidal solutions 

 hold in solution greater quantities of crystalloids than simple solu- 

 tions, for the reason that at the surface of each colloidal particle there 

 is a zone in which the crystalloids are more concentrated than else- 

 where, thus permitting more crystalloids to be dissolved in the solvent 

 between the colloidal particles. On the other hand, the concentra- 

 tion of the crystalloids on the surface of the colloidal particles causes 

 the colloids to serve as the starting point of precipitation whenever 

 the crystalloids are in excess. When the crystalloid goes out of 

 solution, therefore, it will form crystals or precipitates which are 

 most intimatel}^ associated with the colloids, as we see when uric acid 

 crystallizes out of urine, taking with it the colloidal pigments by 

 which it is adsorbed. Or, if the colloids are precipitated, the solvent 

 power of the solution is reduced, and the crystalloids will deposit in 

 intimate relation to the colloids. As Schade pointed out, if a colloid 

 precipitates in an irreversible form (e. g., fibrin), the concretion will 

 be permanent, as with ordinary concretions, but if the colloid pre- 

 cipitate is reversible the mass may be dissolved again, as Avith the 

 precipitate of urates in the tubules of the infant's kidney. 



BILIARY CALCULI 55a 



As may be judged from the above statements, concretions are never 

 composed of one substance in a pure form, but usually consist 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 (piantities several or all of the constituents of the bile. AVliile 

 cholesterol 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 (car- 

 bonate and phosphate) are also present, as well as small amounts of 

 fats, soaps, lecithin, mucus, and other products,'''^'' and occasionally 



55 See Schade, Miindi. med. Woch., 1000 (.5(1). :] -. litll (r)S), r2■^■. Zoit. oxp. 

 Path., 1010 (8), 02: also Lichtwitz, Krgcb. inn. MchI., I!)14 (i;{), 1; also his nionn- 

 grai)h "Lecher die Hil(hin<r dcr ilani- und ( Jallenstcino," Spriiifier, Berlin. 1!>14. 



5-.a Bi),lio;,rrapliy liy Haciiicislcr, Kr;,^^!). inn. Mod.. l!)l:? (11), 1. 



r,ob Fischer and Kosc found about 0.1 <im. carotin in 12S() jiins. >,'all stones from 

 cattle. (Zeit. physiol., Cheni., li)13 (8S), 331.) 



