Iodothyrin

1. A peculiar substance obtained from the thyroid gland, containing from nine to ten per cent of iodine.
   

It is a very stable compound, and is believed to be active principle in thyroid extracts and in the internal secretion of the thyroid gland. It was originally called thyroiodin.

It is probably an impure extract of thyroid gland, containing thyroxine. See Merck Index 11th Ed. #9345, the entry for thyroidin.