Among many distinguished visitors who have adored the Hosts was St. John Bosco. They were likewise venerated by Pope John XXIII, who signed the album of visitors on May 29, 1954, when he was still the Patriarch of Venice. And although unable to visit the miraculous Hosts, Popes Pius X, Benedict XV, Pius Xl and Pius Xll issued statements of profound interest and admiration.
With a unanimous voice, the faithful, priests, bishops, cardinals and popes have marveled at and worshiped the holy Hosts, recognizing in them a permanent miracle, both complete and perfect, that has endured for over 250 years.
By this miracle the Hosts have remained whole and shiny, and have maintained the characteristic scent of unleavened bread. Since they are in such a perfect state of conservation, maintaining the appearances of bread, the Catholic Church assures us that although they were consecrated in the year 1730, these Eucharistic Hosts are still really and truly the Body of Christ. The miraculous Hosts have been cherished and venerated in the Basilica of St. Francis in Siena for over 250 years.http://www.therealpresence.org/eucharst/mir/siena.html