Fluorides were used as insecticides, and occasionally as rodenticides, before their value as preventives of dental caries was known. The organic fluoride rodenticide "1080" differs in pharmacologic action. Inorganic fluorides are only moderately poisonous as such things go, and poisoning in man is a rarity, a gram or more being needed to be lethal in a single dose. Fluorine-containing anesthetics have introduced a whole new interest in medical fluorine, but their chemistry does not cross over into the pharmacodynamics of inorganic fluorides.
The discovery of the action of fluorides in preventing dental caries took place in the field of epidemiology, not in an area of experimentation or pharmacologic investigation. Perhaps this feature was responsible for the slow and reluctant acceptance of the observations by many and for the obstinate opposition of a few. Lingering doubts still find expression among the uninformed. Excessive fluoridation of drinking water produces mottled enamel of