Von Dungern described an alkaline indigo solution that when added to an inactivated serum would inhibit its normal coagulation by heat. He believed that the indigo present was the active inhibiting substance. We have shown that neither the indigo nor the salt content of the reagent takes part in the inhibition of the coagulation. The alkali is the sole inhibiting agent.
Von Dungern further stated that with similar amounts of the reagent this inhibition was less marked in syphilitic than in normal sera. In our experience such a difference was present in but very slight degree and with no constancy.
The method is of no value in the serum diagnosis of syphilis for in our entire series of 140 sera, 40 of which were evidently syphilitic, coagulation occurred n but 3, with the prescribed amount of reagent.