Abstract
IT HAS been known for many years that a reciprocal relation appears to exist between the levels of circulating thyroxin and thyrotrophin in the vertebrate species so far investigated. Until recently, however, direct tests of thyroid activity in man have not been feasible. Within the last few years, radioactive iodine has provided a new method for the study of thyroid function, permitting observations that would otherwise be impossible. Using shielded G–M counters, it is possible to follow directly the accumulation of radioiodine in the thyroid gland. Studies in several clinics have indicated that this method is an accurate index of . . .