1. A METHOD FOR MEASURING THE PROTEIN-BOUND IODINE CONTENT OF THE BLOOD CHARACTERIZED BY THE STEPS OF CHEMICALLY TREATING A BLOOD SAMPLE, PRECIPITATING THE PROTEIN OUT OF SAID SAMPLE, CHEMICALLY TREATING THE REMAINING SUPERNATANT FLUID, AND VISUALLY COMPARING SAID SUPERNATANT FLUID WITH CERTAIN KNOWN STANDARD SOLUTIONS, SAID FIRST CHEMICAL TREATMENT COMPRISING ADDING TO SAID BLOOD SAMPLE SULPHURIC ACID, AN ALKALI METAL SALT, ARSENOUS OXIDE, AN ALKALI METAL HYDROXIDE, SODIUM TUNGSTATE AND WATER, SAID SECOND CHEMICAL TREATMENT COMPRISING ADDING TO SAID SUPERNATANT FLUID A CERIC SALT, SULPHURIC ACID AND WATER.