Once in the skin, the allergen may produce a classic immune wheal and flare response (a skin lesion with a raised, white, compressible area surrounded by a red flare).
In the case of a mosquito attack, many bites will follow the first and swollen hives or a wheal may begin to develop within minutes of the bites.
The physician looks at the injected area 20 minutes later; if it is red, with a raised area (wheal) in the center, the reaction is positive.
Crystals were first found in Cornwall (at Wheal Jane, near Truro, associated with pyrrhotite) by J.
At Wheal Cock near St Just in Cornwall the protecting roof was so thin that holes bored for blasting more than once penetrated to the bed of the ocean, and wooden plugs were kept on hand to drive into such holes when this occurred.