The same uterus may react to one semen by contraction; to another by relaxation. The same semen may contract one uterus and relax another. From this we may draw the tentative conclusions that certain types of sterility are sometimes due to the female, sometimes to the male. A study of the history of the patients from whom uterine strips were obtained throws an interesting light on our experiments. The uteri from the patients who give a history of successful pregnancy responded to fresh semen by relaxation, while uteri from women who gave a history of complete or long-standing sterility were always stimulated by semen. A tentative deduction is permissible : Uteri are of 2 kinds, receptive and rejective; semina are also of 2 kinds, stimulant and depressant. A large series of carefully selected cases will be studied, with the purpose of criticising these deductions.