"Opposition to vote on same terms as men, our constitution was violated, politics of Women's Enfranchisement League" Read the full letter
Gustav Spiller (1864 - 1940) was the Secretary of First Universal Races Congress. Schreiner received an invitation to attend and speak, and she sent a letter of support. Schreiner most certainly corresponded with Spiller and a letter from him to her is extant; however, none of her letters to him have been traced.
For further information see
G. Spiller (ed, 1911) Inter-Racial Problems London: P.S. King & Son