Parafollicular cells in the normal human thyroid

NONIDEZ¹ has described argyrophyllic, granulated cells distinct from follicular cells in the dog thyroid. It is now known that the mammalian thyroid is a source of calcitonin², and the parafollicular cells seem to produce thyrocalcitonin^3,4. Although calcitonin activity has been demonstrated in human thyroid tissue⁵, the parafollicular cells of the human thyroid have never before been demonstrated. Their presence has been assumed, however, because medullary carcinoma of the thyroid consists of cells resembling the parafollicular cells of other mammalian species, and contains calcitonin activity⁶.