On the Kinetic and Invasive Power of Regen- Erating Tissue and on Similarities in the Behavior of Thyroid Transplants and Carcinomas

In the course of a study of the factors which determine regeneration of the thyroid gland and the fate of thyroid transplants, we compared autotransplantation of one thyroid lobe in cases in which the second lobe had been left intact and in which it had been extirpated previous to the transplantation. We also compared the fate of autotransplants and homoiotransplants at various stages. In an animal, a female guinea-pig (no. 758) weighing 370 grams, we transplanted one lobe of the thyroid subcutaneously into the same animal. The lobe of the other side was left intact. Seven days later the transplant was taken out for examination. The recovered piece was relatively large and cut into serial sections. Microscopic examination showed the following : A connective tissue capsule rich in fibroblasts surrounds the piece; it encircles a ring of acini, which, however, is not complete, being interrupted at such places where fat tissue constituted the periphery of the transplant. The peripheral mini are the larg-