1. In cats atropine given before or after DFP abolished the "muscarinic" symptoms, reduces or abolishes the central excitant effects, and provides marked protection against the fatal action of DFP.
2. Magnesium controls the fibrillary twitches of skeletal muscle caused by DFP, but alone affords but slight protection against the fatal action of DFP.
3. A considerable further degree of protection against DFP is afforded by the simultaneous use of magnesium and atropine.
4. The results indicate that DFP causes death by two mechanisms, one of which is blocked by atropine, the other brought on by larger doses is blocked by magnesium.