1. Human thyroid tissue may be kept alive and in good condition in the Lindbergh apparatus for at least 3 weeks, in usable condition from 1 to 2 months, provided that the vascular tree remain patent and functioning.
2. Experiments with altered amounts of iodin, adrenalin, hormones, and other substances show constant results only in connection with eschatin and pitressin which, in concentrations of 1:1000 in the perfusate almost invariably cause hyperplasia of the explanted tissue.
3. The original state of the tissue and the character of the symptom complex in the patient from which it was taken appeared to play no part in the subsequent behavior of the tissue explants.
4. In one experiment a most remarkable metaplasia was observed in the explanted thyroid tissue during the 6 to 8 weeks that it remained in two apparatuses. The cause of this is not evident.