2. Ten samples of serum obtained from three adult female monkeys at various phases of the menstrual cycle likewise proved incapable of neutralizing the virus. An eleventh serum, drawn from a fourth female 32 days postpartum, gave irregular results. It neutralized once and failed to do so on second test. This is the only suggestion in our experiments that a physiological factor may play a part in poliomyelitis immunity.

3. Fourteen sera from ten immature monkeys caused to menstruate by treatment with anterior pituitary extract were devoid of virucidal property. This treatment failed also to induce a systemic resistance to intracerebral injections of virus in the nine monkeys of the same group available for test.

4. We were unable to demonstrate in our monkeys a correlation between virucidal capacity of the serum and maturity or physiological variations as exemplified by menstruation.