The adrenal cortico-medullary ratio in the fowl.

1. A new integrating method of assessing the proportions of cortical and medullary tissue in the avian adrenal gland is described and statistically evaluated. 2. It is shown that a single "central" section of the adrenal gland will suffice to obtain accurate results. 3. Each section was projected on to a grid of about 2500 intersection points and the ratio of points falling on cortical or medullary tissue was determined. 4. Applications of this method to normal fowls showed that there were significant breed, sex and, particularly, age differences in the cortico-medullary ratio of the fowl's adrenal glands.