Crabs’ eyes
Lapides cancrorum, oculi cancrorum
- Known today as
- Chalky stones from the stomachs of crayfish.
- Kind
- Animal, in 2 older authorities
- Constituents
- calcium carbonate, calcium phosphate, chitin
- Earliest authority here
- The German pharmacy
Revised October 1, 2026: Tradition, lore, modern assessment, and sources extended. Version 1, first published September 25, 2026.
Crabs’ eyes: what was it used for?
“Absorbents”: for acidity, heartburn, and fevers.
Crabs’ eyes: what does modern science say?
They are calcium carbonate, a real antacid, so the remedy worked for heartburn. Calcium carbonate neutralises stomach acid, so the heartburn remedy was a sound one, the same as chalk and the antacid tablets of today; for fever it did nothing.
Pharmacognosy & Toxicology
- Constituents
- calcium carbonate ChEMBLamorphous and calcite
- calcium phosphate ChEMBL
- chitinthe matrix
- Mechanism
- The gastroliths of the crayfish, stored calcium for its new shell after the moult: a chalk antacid, and nothing else. They were in the London Pharmacopoeia through the eighteenth century as an “absorbent” for acidity, which they are.
- Toxic dose
- Inert.
- Standing
- Obsolete; the gastrolith is now studied for its amorphous calcium carbonate as a bioavailable calcium supplement.
- Luquet, G. (2012). “Biomineralizations: insights and prospects from crustaceans.” ZooKeys 176. Verified against its record · doi:10.3897/zookeys.176.2318
The abstract of each source, beneath its citation. For Club members. About the Club or sign in.
Constituent names open the compound’s record at PubChem, and “ChEMBL” beside a name opens its record at ChEMBL, the European Bioinformatics Institute’s database of bioactive molecules. Where a mechanism line was checked against ChEMBL (ChEMBL 37, read 1 October 2026), the check is shown with the measured value and its source paper, or says plainly that nothing has been measured. Doses are as the references give them, for description only; this is not medical advice. Each source carries the result of its check against Crossref, PubMed, or the authority’s page: see Verification.
Crabs’ eyes: what lore surrounds it?
They are not eyes but gastroliths, flat buttons of lime; the name came from their look,. The pulvis e chelis cancrorum, of crabs’ claws, was the companion powder.
Crabs’ eyes: what did the older authorities say?
- The German pharmacy
- Lapides cancrorum were gathered from the stomachs of crayfish in the rivers of Bavaria and Bohemia, where the animals store lime before moulting, and were sold by the pound to the apothecaries of Europe; the Dutch prepared them by levigation into a white powder.
- Culpeper
- Gives them, with coral and pearl, among the absorbent powders for the sour stomach, the heartburn, and the fevers of children.
Sources
- Culpeper, N. (1653). Pharmacopœia Londinensis. Read in full · the text read
- Pomet, P. (1694). Histoire générale des drogues. Book, seen in reviews
Verification
- Checked
- October 1, 2026
- Passes
- Every sentence read against its sources, in the fifty-entry sample
- The Standing line checked against the authority it names (EMA, WHO, FDA, CITES, Commission E)
- Every dated or regulatory claim checked by category across the database
- Sources
- 3 cited: 1 read in full, 1 verified against its record, 1 book, seen in reviews. 1 with the abstract on file.
- Corrections
- said they are still sold in the markets of Prague. No source; removed. Also "London Pharmacopoeia into the nineteenth century" softened to the eighteenth.
What was checked, how, and what was found is set out on the Verification page. A checked source is one whose record was found; it does not make the entry medical advice.
Cite This Entry
Version 1 · first published September 25, 2026 · last revised October 1, 2026
- Chicago
“Crabs’ eyes.” In Materia Medica, edited by B. C. P. Statema. Version 1. The Thinking Press, 2026–. Last modified October 1, 2026. https://thethinkingpress.org/materia-medica/crabs-eyes.
- MLA
“Crabs’ eyes.” Materia Medica, edited by B. C. P. Statema, version 1, The Thinking Press, 1 Oct. 2026, thethinkingpress.org/materia-medica/crabs-eyes. Accessed 8 Oct. 2026.
- APA
Crabs’ eyes. (2026, October 1). In B. C. P. Statema (Ed.), Materia medica (Version 1). The Thinking Press. Retrieved October 8, 2026, from https://thethinkingpress.org/materia-medica/crabs-eyes
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See Also
Sharing calcium carbonate, calcium phosphate, chitin
Cuttlefish bone · Corallium rubrum · Olive-wood ash lye · Woodlouse · James’s powder · Lepidotes
Also in Nicholas Culpeper
Devil’s-bit scabious in Nicholas Culpeper · Cowslip in Nicholas Culpeper · Endive in Nicholas Culpeper · Chicory in Nicholas Culpeper · everything Nicholas Culpeper names →
Drawing on the same sources: Culpeper, Pomet
Dandelion · Cubeb · Cochineal · Earthworm · the bibliography →
Nearby in the alphabet
Cramp rings (made from gold and silver offered at the cross) · Crow’s gall (The bile of a crow) · Cornicello · Crucifix (The image of Christ on the Cross) · Corn smut · Coriander (seed and leaf)
Historical description, not medical advice.