A voluminous literature also exists upon this subject. Attacks upon
religion are to be found in such books as Leuba’s “Belief in God and
Immortality,” and Theodore Schroeder’s writings, which endeavor to
trace all religion to sex. On the other hand, are to be found such
books as Barrow’s “The Validity of the Religious Experience,” and
William James’ “Varieties of Religious Experience.” An extensive
study of Mysticism is Poulain’s “The Graces of Interior Prayer.”
The literature on this subject is so vast, however, that it would be
impossible even to indicate the sources of reference.