(Ed. Yet where are they now??)
The contralto is the norm against which the other voices and instruments must be gauged. If you want to do without the contralto you can push the prima donna assoluta as high as the moon, and the basso profondo right down to the bottom of the well. And this will leave you with nothing in the middle. One should concentrate on the central register in order to be always in tune; at the extreme ends, what you gain in force you often lose in grace, and by this abuse you paralyse the throat, resorting as a remedy to canto declamato, that is, out-of-tune shouting. Then it becomes necessary to give the orchestration more body in order to cover the excesses of the voice, to the detriment of good musical colour.
Senici, Emanuele. The Cambridge Companion to Rossini. Cambridge University Press, 2004..