1. In a series of rabbits the changes which took place in the histology of the left lobe of the thyroid gland after excision of the right lobe have been studied at varied intervals of time. 2 days after the removal of one lobe the other lobe showed a slightly increased colloid content, an increased vacuolation of the colloid, and a slight increase in the size of the epithelial cells. At the end of a week the vesicles were greatly increased in size, distended with colloid, and the epithelial cells were flattened, while after 3 to 4 months signs of compensatory hypertrophy were present.
2. The changes observed were uninfluenced by division of the vagus or cervical sympathetic.