The history of the use of thyroid extract in insanity dates back to the year 1893, when McPherson (1), of Larbert Asylum, reported a case of myxódematous insanity which recovered from both the myxódema and the mental disorder under its use. Its use in cretinism has also met with much success. My investigations, however, are confined to its use in mental conditions not associated with myxódema or cretinism. In 1894 McClaughey (2), of the District Asylum, Maryborough, reported two cases as improved, and in 1894–5 McPhail and Brace's results (3) and observations of treatment were published in detail. The publication of their results and their belief that “in thyroid feeding we possess a valuable addition to our armamentarium in the treatment of certain cases of insanity” incited many other alienists to test its efficacy. Besides Clarke, Brush and Burges in America must be mentioned Mabon and Babcock (4), who give a review of the results obtained in 1032 collected cases of insanity from twenty-four different observers, and who show that 23·9 per cent. recovered and 29·4 per cent. were improved. They also report on a further use of thyroid on sixty-one cases at the St. Lawrence State Hospital.