Abstract
Rats 21 days old received single injections (group I) of 25 units of extract, or 5-10 daily injections (group II). Rats of group I killed on the 6th day after injection had a few mature follicles, 2-5 corpora lutea, cornified vaginae, pituitaries showing a slight increase in weight and degranulation of basophiles. Those of group I killed 11 days after injection showed regressive changes. Rats of group II killed 6 or 11 days after beginning of treatment showed more marked changes, which were sustained.