Abstract
The prolonged adm. of pure adrenocorticotrophic hormone caused a characteristic alteration of the ant. pituitary of the young [male] rat. The alteration consisted in a decrease in the wt. of the gland, a diminution in the size of basophils, and morphological and cytological changes which can be characterized as being indicative of a depressed or retarded function. These outspoken changes, obvious in [male][male] 56 days old, were also detectable in adults treated with the hormone for a shorter time, but the changes were less constant and far less pronounced. Acidophils did not show any appreciable evidence of effects from the hormone inj.