Seasonal variations of rat thyroid C cell population.

With the aid of argyrophilic and metachromatic reactions male rats' thyroid C cells were investigated in spring and autumn. Autumn C cells were found to be more swollen and richer in granules and showed a more pronounced metachromasia and argyrophilia than spring C cells. The area occupied by C cells in the central part of the thyroid lobe was large in autumn and reduced in spring. A study into the proportions of C cell: follicular cell: colloid: stroma indicated a significantly higher number of C cells in autumn than in spring.