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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.
Translation. For rapidly developing, or acute diseases, also resolve of their own accord, sometimes through favourable chance and sometimes through nature's favour. Consequently, ignorant people, carried away by this, often avoid physicians and attribute these favourable outcomes to new incantations and amulets, or to chance; for these rapidly developing diseases are driven out either by a flow of sweat, by blood discharged through the nose, or by a discharge from the intestines. But chronic diseases, or diseases of slow development, which have already gained possession of the body with a kind of prior claim, call for the skill of the physician alone, since they are resolved neither by nature nor by chance.
Interpretation. Caelius Aurelianus contrasts spontaneous resolution in acute disease with the entrenched course of chronic disease. Here passiones means affections or diseases, not emotions; ligamenta means protective bindings or amulets, not anatomical ligaments; proventus means favourable outcomes. The metaphor praejudicio quodam gives the established disease something like a prior claim on the body. The final assertion is the author's defence of professional medicine, not a present-day law that every chronic disease requires effective medical treatment or that none can remit spontaneously. The account of sweating, nosebleeds and intestine discharge describes his historical explanation, not evidence that deliberately producing these discharges cures acute disease. [ref]
Examination papers for the Degree of Bachelor of Medicine by the University of Oxford (1864–1867). PDF volume p. 101, Latin extract attributed to the preface to Caelius Aurelianus's chronic diseases