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Incoming links: Bile pigment
The chief historical examples are rhubarb, senna, santonin and logwood for urine; iron preparations, bismuth preparations and charcoal for darkening the faeces. There are two different processes: a substance absorbed and subsequently excreted can colour a secretion, while material remaining in the intestinal lumen can colour the stools without demonstrating systemic drug absorption.
- Rhubarb colours urine yellow to yellow-brown; the colour becomes redder in an alkaline solution. The contemporary account also reports coloration of sweat and breast milk. This is a historical observation about passage of colouring matter, not a claim that every constituent passes unchanged into every secretion. [ref]The Essentials of Materia Medica and Therapeutics by Alfred Baring Garrod (1865). Labiatae, continued, Rheum: colouring constituent, alkaline solutions, and coloration of urine, perspiration and milk
- Senna can give urine a yellow-brown or red-brown colour. The effect is still recognised in current medicinal information. [ref]Senna by the NHS. Side effects, coloration of urine
- Santonin, used historically as an anthelmintic, can make urine conspicuously yellow. This must be distinguished from the drug's separate effect on colour vision: a yellow-looking visual field is not itself excretion of a yellow pigment. [ref]A Manual of Practical Therapeutics by Edward John Waring (1865). §2416, physiological effects and yellow urine
- Logwood can give urine a pink or reddish colour, particularly when it is an alkaline solution; the historical description notes that addition of Ammonia brings out the colour in a previously acid specimen. [ref]The Essentials of Materia Medica and Therapeutics by Alfred Baring Garrod (1865). Cisalpinae, Haematoxylum, urine coloration
- Iron preparations can darken faeces; bismuth preparations also cause dark or black stools. In these examples the result need not be a pre-existing vegetable dye simply passing unchanged through the body. Current information confirms black stools with oral iron and with the modern bismuth medicine bismuth subsalicylate; the latter is corroboration of the colour effect, not an identification of that modern formulation with the 1864 bismuth articles. [ref]Bleeding from the bottom by the NHS. Dark stools and iron tablets[ref]Pepto-Bismol by the NHS. Side effects: black stools and black tongue
- Charcoal supplies a black material directly to the bowel contents. Its appearance in the stools does not require its absorption and subsequent renal excretion.
Colour alone does not identify either the drug or a disease. A medicinal pigment can resemble blood or a bile pigment; pH, timing after administration and appropriate chemical or microscopic examination distinguish possibilities. Conversely, a history of taking a colouring medicine does not prove that an observed specimen contains no blood. These examples describe pharmacological and historical observations, not results from an unseen specimen.
Gallstones contain chiefly cholesterol and/or bile pigment, with variable calcium salts and an organic matrix. They are mixtures with different predominant components, not one compound with a universal formula. The period word cholesterin denotes cholesterol.
Cholesterol-rich stones contain crystalline cholesterol, often with a smaller pigmented nucleus and layers of other material. Mixed stones combine cholesterol, pigment, calcium salts and an organic matrix including mucin. Pigment stones contain much less cholesterol; a major constituent is calcium bilirubinate, related to the bile pigment bilirubin. Minor inorganic constituents can include calcium carbonate and calcium phosphate. Not every visibly dark stone has the same composition, and no fixed percentage follows from the question.[ref]
Gallstone Composition by Merck Manual Professional Edition. Cholelithiasis: cholesterol, black pigment and brown pigment stone composition
The useful modern subdivision of pigment stones is into black and brown types. Black stones commonly contain polymerised pigment with calcium salts; brown stones include calcium bilirubinate and calcium salts of fatty acids, particularly in infected stagnant duct bile. These refinements explain why neither “all stones are cholesterol” nor “all stones are lime salts” is adequate.[ref]
Gallstones by NIDDK. Definition and facts; symptoms and causes: cholesterol, bilirubin and bile composition
Chemical examination should distinguish the fractions rather than infer them merely from the external colour. Cholesterol can be extracted with a suitable organic solvent and recognised in recrystallised material; microscopy can show characteristic plate-like crystals. A mineral residue after removal or destruction of organic matter indicates an inorganic fraction, but residue alone cannot identify a particular salt. Layering, facets and colour describe growth and packing and are not chemical analyses. In particular, calcium bilirubinate is not interchangeable with calcium carbonate, and cholesterol is not a bile salt.