1. A certain dose of apomorphine and caffeine inhibits the sexual cycle in the albino rat.
2. Atropine administered in a certain dose has no influence on the inhibitory effect of either one of these two drugs, but luminal and urethan suppress almost completely the inhibitory action of these drugs, especially it has a reversal effect on the action of caffeine.
3. This prolongation of the sexual cycle seems to be due to the primary excitation of the cerebral cortex and subsequently that of the diencephalone, and aside from its inhibitory action caffeine has an accelerating effect and under normal conditions the former effect seems to predominate the latter.
4. It is to be concluded that the cerebral cortex is intimately related to the sexual cycle in the albino rat and its excitation inhibits the sexual cycle.