Where to find Pius IX's 1871 Apostolic Letter, "Qui Ecclesiae Suae"?

The following quote is from Pope Bl. Pius IX's declaring St. Alphonsus Liguori as a Doctor of the Church: >“One can in fact assert that there has not been one error even in our times which Alphonsus, at least in great measure, did not fight against.” (Source: *Qui Ecclesiae Suae*, Apostolic Letter, Pius IX, Rome, 1871.) Can anyone provide me with a link to the papal document *Qui Ecclesiae Suae*? I thought it would be an easy thing to find, but I was mistaken.