Red deer bladder 
Urinary bladder of a red deer stag (Cervus elaphus), obtained from hunting and dried.
Characteristics
- In biodynamics it is the casing of preparation 502 (yarrow).
- Once dry it keeps for a long time and is soaked again before filling.
- The filled bladder hangs in the sun in summer and is buried in autumn.
Role in the preparation: It serves as a natural casing while the preparation matures.
Caution: Source it from hunters or approved game dealers and follow animal-health rules on game by-products.
Sources: Biodynamic agriculture - Wikipedia · Red deer - Wikipedia
Documentary information: this is neither a recommendation for use nor a plant-protection or veterinary claim. Check your country's regulations before any use.