Dystrophies due to chronic fluorine poisoning in organs regulated by the parathyroid glands, namely the skin and its appendages, the nails, teeth and hair, and also in bones, are here shown to be unusually common in this country. They should be regarded as easily detectable signs of a serious disturbance of the calcium metabolism of the body. Fluorine is a poison of which the action, in many respects, is similar to that of arsenic. It is the task of the authorities responsible for the health of the nation to search for ways and means capable of minimizing its effect.I wish to express my sincere thanks to the Librarian of the Royal Society of Medicine and his staff for their never-failing courtesy and help.