C cell follicles in the dog thyroid: Demonstration by in vivo perfusion

The histology and ultrastructure of the parafollicular cells of eight dog thyroids were studied by various methods of fixation. The best preservation resulted from in vivo perfusion with glutaraldehyde. When prepared in this manner clusters of C cells were seen to possess follicular and canalicular systems. Coated vesicles were noted at various luminal surfaces and at the basilar plasma membrane. The authors conclude that the maintenance of intracapillary pressure during fixation is essential for the demonstration of normal histological and ultrastructural anatomy of the thyroid.