See, e.g., Shattock and Seligmann, "The Acquirement of Secondary Sexual Characters," Proceedings of the Royal Society, vol. lxxiii, 1904, p. 49.
For facts bearing on this point, see Guinard, art. "Castration," Richet's Dictionnaire de Physiologie. The general results of castration are summarized by Robert Müller in ch. vii of his Sexualbiologie; also by F. H. A. Marshall, The Physiology of Reproduction, ch, ix; see also E. Pittard, "Les Skoptzy," L'Anthropologie, 1903, p. 463.
For an ancient discussion of this point, see Schurig, Spermatologia, 1720, cap. ix.
J. J. Matignon, Superstition, Crime, et Misère en Chine, "Les Eunuques du Palais Impérial de Pékin," 1901.