The toxicity of fluorine compounds once considered of little general importance is no longer so regarded. The increasing use of fluorides as insecticides, the discovery that fluorine may be a component of many foodstuffs and the work of Dr. Margaret Cammack Smith and associates (77·88) in proving that potable waters containing as little as 0.9 parts per million of fluorine may produce mottled teeth in growing children when regularly ingested over periods of several years, has excited much popular as well as scientific interest in fluorine toxicoses. Ostrem, Nelson, Greenwood and Wilhelm (55) have shown that this mottling of teeth is endemic in certain sections in Iowa.