Between the end of the eighteenth and the beginning of the nineteenth century, the shortage of castrati among available opera singers compelled coeval composers to contrive substitutes for the roles of "primo musico" in operatic companies. The solution that seemed the most immediate and the most according to tradition, was the so-called "contralto musico", or female singers—usually mezzo-sopranos rather than real contraltos—who could perform the roles originally written for castrati as well as the parts composed with female singers in mind. According to Rodolfo Celletti, in the first 35 years of the 19th century, more than 100 cases of original resort to the "contralto musico" can be counted up, and it was employed also by musicians of the rising post-Rossini generation, such as Donizetti, Mercadante, Pacini and Bellini.