The collapse of Cassava Sciences and a resounding fall in the stock .
Cassava Sciences shares fall sharply as market opens It dropped more than 80% on Monday .
This strong and violent decline comes after the company announced its failure In an experiment to treat low-and moderate-grade Alzheimer's disease .
The company has announced that it will stop the second phase III trial .
The experiment involved 804 people in America, Australia and Canada .
