A snake-stone, also known as a viper's stone, black stone, schwarze Steine, pierres noire, piedritas negras or serpent-stone, nagamani is an animal bone or stone used as folk medicine for snake bite in Africa, South America, and Asia.
The early Celtic era European Adder stone is also called a snake stone, and is usually made from coloured glass, often with holes. Its purpose is for protection against evil spirits rather than snake bite.
Experts are concerned that relying on a black stone may prevent snakebite victims from seeking appropriate medical help. No scientific study has shown that black stones per se are effective, but, most guidelines for snakebite first-aid stress the need for keeping the victim calm (because acute stress reaction increases blood flow and endangers the victim, and panic is infectious and can compromise judgment).
Accounts differ widely on how to make and use a 'black stone'.
In Peru, a black stone is a small charred cow bone, "applied to the site of a poisonous snakebite and tied firmly in place. It is left there for several days, during which time it supposedly draws the venom from the wound."
Persian/Iranian writer Kazwini describes the snake-stone as being the size of a small nut. An injury inflicted by a venomous creature is to be immersed in warm water or sour milk. The snake-stone is then dropped into the liquid to supposedly draw out the poison.
The steps suggested in an African leaflet are:
- Choose a large dry cow thigh bone
- Cut it into small pieces
- Smooth them with sandpaper
- Wrap the pieces in foil
- Place in a charcoal fire for 15 to 20 minutes
Views on snake-stones expressed in scientific studies
A Nigerian study recommended "education on the need to avoid the use of popular first aid measures of doubtful benefit." The same doctors later reported that Black Stones may be beneficial, but "those who used the black stone required significantly higher quantity of antivenom as compared to those that used the tourniquet". In their report they noted slightly higher tissue necrosis in patients who use tourniquets, but this was not (statistically) significant; other scientists have recommended against tourniquets (see treatment of snakebites and outdated treatments).
An Indian study stated, "unscientific methods like ‘black stone’ healing contribute to the delay in seeking appropriate medical care."
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