Studies in Thyroid Transplantation. 203 



stump, and in addition a simultaneous and similar degree of 

 hyperplasia of any existing transplants independent of their 

 location. Thus we have seen such reactions in ovarian, adrenal 

 and subcutaneous transplants of the chest, neck and abdomen. 



Now, if one gives very small doses of some idoin-containing 

 substance, whether by mouth or by the use of a little tincture 

 of iodin as in skin sterilization, involution promptly occurs in 

 from two to three weeks which effects the transplants irrespective 

 of their location in the same way as the main thyroid gland stump 

 is effected. We have seen no exception to this except in cases 

 where the total amount of thyroid tissue was below the level at 

 which iodin will protect against thyroid hyperplasia. Also if iodin 

 is administered prior to or at the time of transplantation, no 

 hyperplasia of either the original gland or transplants occurs until 

 the effect of the iodin has fallen to the level of inducing an in- 

 sufficiency. Likewise if iodin is administered following trans- 

 plantation, no hyperplasia ordinarily occurs during the time of 

 such administration. We have followed such thyroid transplants 

 for as long as 271 days. 



If now a large part of the transplanted thyroid tissue and of 

 the original gland, thus involuted, is removed, the remaining thy- 

 roid transplants and the remaining portion of the stump 

 undergo active hyperplasia for the second time. This is similar 

 in all essentials to the effects seen in dogs following alternate 

 partial thyroid removals and iodin administrations. There is 

 evidence also that transplanted thyroid tissues function. We 

 have observed four rabbits showing marked amelioration of the 

 symptoms of operative myxedema associated with active hyper- 

 plasia of subcutaneous abdominal transplants. 



In view therefore of the facts that (1) under favorable condi- 

 tions thyroid tissue may "take" and grow in widely different 

 parts of the body; (2) that such transplanted tissue undergoes 

 hyperplasia simultaneously and is histologically identical with 

 that of the original gland stump; (3) that iodin induces an involu- 

 tion alike in both the transplanted and non-transplanted tissue, 

 we believe (a) that the thyroid may function as a true blood- 

 vascular gland in that the stimuli which cause these hyperplasias 

 may reach the gland cells through the blood stream and that 



