This short treatise was written for the benefit of those who cannot devote much time to the study of the Index. It appeared first in the “Catholic union and Times,” Buffalo, N. Y., and was reprinted in the “Catholic Mind” series, Fordham University Press, New York, as numbers 23 and 24 of 1907.  
Those who wish to make a deeper study of the subject are referred to the following books:
 
Rev. Timothy Hurley.—A Commentary on the Present Index Legislation. Dublin, Brown and Nolan. New York, Benziger Bros. $1.35.
Rev. Arthur Vermeersch, S.J.—De prohibitione et censura librorum. $0.85.
Rev. Jos. Hilgers, S.J.—Der Index der verbotenen B&uum............