1879.] Influence of Colloids upon Crystalline Form, §c. 243 



ment. The light radiating layer (3) is composed of nearly colourless 

 crystalline columns of cholesterin radiating as from the centre of the 

 calculus, with accumulations of pigment in the spaces between them ; 

 while the centre (4) is nearly all deep brown pigment, actually black 

 in some cases, mixed here and there with perfectly formed, thick, 

 colourless, rhombohedral slabs of cholesterin. The explanation of this 

 composite structure appears tolerably easy by the light of the experi- 

 ments recorded. The cholesterin is first deposited in the pigment with 

 or without some mucus. These, the colouring matter in particular, 

 are substances of high molecular composition, and when first secreted 

 in the bile are most typical colloids. But when kept outside the 

 body, or retained for any length of time within it, the bile-pigments 

 slowly exchange the colloid for the crystalline state, and may often be 

 seen in rhombohedral forms of great beauty in hydatid cysts in the 

 liver. In proportion as the pigment is relatively abundant at the 

 time of the precipitation of the cholesterin the latter is more com- 

 pletely fused and intermixed with it. The superficial part of the 

 calculi, of course the latest deposit, shows this intermixture. The 

 concentric layers show a commencement of rearrangement of particles 

 subsequent to deposit. Here the cholesterin and pigment are be- 

 ginning to separate from each other, and the lines of crystallisation 

 are already related radially to the centre of the calculus. The calculus 

 exhibits on a large scale the mingling concentric and radiant arrange- 

 ment of molecules seen in the small spheres of carbonate of lime and 

 other salts formed by Mr. Rainey, and in the small spheres found on 

 the surface of the calculi under investigation (see fig. 30). In the 

 light-coloured radiating layer (3) separation has gone further ; crys- 

 talline fibration has been exchanged for strongly-marked angular and 

 columnar form, and the colour is nearly all interstitial to the crystals, 

 while the whole arrangement is again clearly related to the centre of 

 the whole sphere. Lastly, in the very centre (4), where all lines of 

 attraction are balanced, the pigment accumulates in quantity, and the 

 few crystals left are independen and typically perfect in form. The 

 result of the investigation is to the remarkable effect that a meta- 

 morphic change is in process within the calculus from the time of its 

 first formation up to the time at which it is submitted to examination, 

 involving a constant rearrangement of particles in relation to the 

 centre of the whole mass, and dependent upon the double tendency 

 seen in cholesterin under experiment : first, the tendency to be de- 

 posited in the spherical form when precipitated in a colloid matrix ; 

 second, the tendency to revert, in process of time, to a crystalline form : 

 the molecules in their passage from the one state to the other being 

 caught, as it were, by the common attraction of the great sphere, and 

 brought to a certain extent under their dominion. The fact that the 

 colloid forming the matrix is one which tends ultimately to become 



