“…When the estrone was administered over a 2-day period and the vaginal smears were taken on the afternoon of the 3rd and morning of the 4th days, testosterone propionate (TP) was an estrone blocker, whereas neither progesterone, desoxycorticosterone acetate (DCA)nor cortisone acetate was active (Edgren, 1960a). If, on the other hand, the estrone were administered over a 4-day period, progesterone and DCA, as well as TP were blockers, (Edgren, 1960b); the smears were taken on the afternoon of the 5th and the morning of the 6th days. In this 2nd study the time of administration of the blocker proved important.…”