Toad-stones - 'Bufonius lapis'

A man extracting the jewel from a toad's head; 
two 'jewels', already extracted are seen dropping to the ground. 
From the 'Hortus Sanitatis', published in 1490

Toad-stones - in Latin 'Bufonius lapis' - were thought to have 
marvellous power. A Polish physician named Jonstonus writes in 1657:

'Toads produce a stone, with their own image sometimes. It hath very 
great force against malignant tumours that are venomous. They are used 
to heat it in a bag, and to lay it hot, without anything between, to the naked 
body, and to rub the affected place with it. They say it prevails against 
inchantments of witches, especially for women and children bewitched. 
So soon as you apply it to one bewitched it sweats many drops. 
In the plague it is laid to the heart to strengthen it'

A magical talismanic ring set with a toadstone was
believed to protect the wearer from harm, especially
poison. Not a stone from the head of a toad at all
but the palatal tooth of a fossilised fish, a ray

Salisbury Museum, UK