Squeeze a drop of juice from the mushroom onto absorbent, high lignin content paper (newspaper). Stool or gastric sample should be diluted with methanol, spun and filtered.
Mark the perimeter of the spot with a pencil
Dry the spot
Add 2 drops of concentrated hydrochloric acid to the area.
If the paper goes blue it indicates the presence of amatoxins. A control drop of acid can be added to another area of the paper.
The reaction may take up to 20 minutes for trace amounts of toxins