BILIARY CONCRETIONS. 575 



2. The second kind are polygonal, because a number of them 

 exist in the gall-bladder at the same time, which causes them to 

 affect each others shape. Externally they have a covering com- 

 posed of thin concentric layers ; within, a matter either crystal- 

 lized, or having the appearance of coagulated honey. They 

 consist of cholesterin mixed with some choleic acid, probably a 

 little modified in its nature. They vary considerably in their 

 specific gravity : one examined by Br Bostock had a specific gra- 

 vity of 0-900* The mean specific gravity of six which I ana- 

 lyzed was 1-061 ; and they all sunk in water. 



These calculi, in their composition, differ but little from the 

 last species, since they consist almost entirely of cholesterin. In 

 six gall-stones which I analyzed, this matter amounted to at 

 least ]ths of the whole. The residue was a reddish-brown sub- 

 stance insoluble in alcohol. Nitric acid dissolved it readily, and 

 formed a pink-coloured liquid, from which ammonia threw down 

 no precipitate. Pure potash ley dissolved most of it readily when 

 assisted by heat. From the solution, muriatic acid threw down 

 a dark-green matter, which had a bitter taste, dissolved in alco- 

 hol, melted when heated, and exhibited most of the properties of 

 choleic acid, The residue, insoluble in potash, was in grey 

 flakes, and resembled albumen in such of its properties as could 

 be traced. But as it never exceeded Jth of a grain, it was not 

 possible to ascertain its nature with precision. 



3. The third kind have a brown colour, and an irregular shape. 

 They are composed of inspissated bile. They are much more 

 common in the gall-bladders of the inferior animals than in that 

 of man. 



4. The fourth kind comprehends those gall-stones which do 

 not flame, but gradually waste away at a red heat. Very little 

 is accurately known respecting this kind of calculus. Dr Saun- 

 ders tells us that he has met with some gall-stones insoluble both 

 in alcohol and oil of turpentine ; some of which do not flame, but 

 become red, and consume to an ash like a charcoal.f Haller 

 quotes several examples of similar calculi. :f Probably they do 

 not differ from the third kind. Two calculi of this kind, very 

 different in their composition, described and analyzed by Orfila 

 and Bally, and Henry, Junior, will be noticed below. 



In 1820, M. Vogel examined a human biliary calculus of un- 



* Nicholson's Jour. iv. p. 136. f On the Liver, p. 112. 



f Physiol. vi. p. 567. 



