Most of the important singers of the present (c. 1855) owe their talent more to fortunate natural endowment than to their training. This is true of Rubini, of Pasta, and of many others. The true art of bel canto ended with the disappearance of the castrati; one must agree to that, even if one cannot wish to have them back. Their artistry was all that those people could have, and so they devoted the most assiduous diligence and untiring care to their training. They always turned into able musicians, and when their voices faltered, they were at least excellent teachers.
Weinstock, Herbert. Rossini: A Biography. NY, 1968, p. 264, quoting Hiller, Ferdinand: Aus dem Tonleben unsere Zeit, in 2 vols., vol. 2. Leipzig, 1868.