The alternatim practice is one of the oldest and longest observed liturgical practices in the French Catholic Church. With the gradual addition of the organ to the practice beginning in the fifteenth century, the organ came to play an important liturgical function that exists to this day. Organ improvisations in the liturgy gave rise to composed organ masses such as those of François Couperin (1668-1733). Composition of the Baroque organ mass continued through the Classical period and into the nineteenth century. Liturgical and musical changes through the decades of the nineteenth century, however, led to a gradual cessation of the composition of organ masses. These same changes gave birth to a new type of liturgical mass that, while not performed in the traditional alternatim style, displayed stylistic and liturgical influences from the Baroque organ masses of the preceding centuries. Messe, op. 4, of Camille Saint-Säens (1835-1921) was composed in 1856 in the midst of nineteenth-century changes and reforms. This mass is the pivotal event between the masses of the preceding generation and those that were to follow, notably those of Charles-Marie Widor (1844-1937) and Louis Vierne (1870-1937). Because the viva-voce presentation of this document featured a performance of Louis Vierne's Messe solennelle, op. 16 using a solo organ edition of the work, Appendix A includes considerations for the work as well as an overview of four solo editions.