Kottmann1 in 1920 demonstrated a reaction in human blood serum which he asserted varied with the activity of the thyroid. The increased or decreased function of the gland was assumed to affect the protective colloidal properties of the blood serum of the patient, and this property, in turn, to affect a certain photochemic reaction of the serum. By means of this, according to his hypothesis, the thyroid activity could be measured.
The technic of the Kottmann reaction is essentially as follows: To 1 cc. of fresh unhemolyzed serum in a small Wassermann type test tube, 0.25 cc. of 0.5 per cent potassium iodide is added, then 0.3 cc. of 0.5 per cent silver nitrate, and the tube shaken after each addition to insure uniform mixing. The tube is then exposed to a 500 watt mazda lamp at a distance of 25 cm. for five minutes, at the end of which,