Only on books and on their correspondence did they spend freely.

Giovanni was preparing a work on reason in Christian morality.

His wife read for him, made extracts, took notes.
"I should so much like to go to Hergyswyl next summer," said she, "that you might write the last chapter of the book there, the chapter on Purity!" So saying, she clasped her hands, happy in the vision of the little village, nestling among the apple trees at the head of the tiny bay, the calm lake, the great religious mountains, the quiet days, spent in work and peaceful contemplation.

She was acquainted with the entire plan of her husband's work, with the subject of each chapter, with the principal arguments.
The chapter on Purity was her favourite because of its rational trend.
In it her husband intended to propose and to solve the following problem: "Why does Christianity exalt, as an element of human perfection, that renunciation which subjects man to fierce struggles, is of no benefit to any one, and closes the door of existence to possible human lives ?" The answer was to be deduced from, the study of the moral phenomenon in its historical origins, and its development; to this study the first two chapters of the work were dedicated.

Selva showed by the example of the brutes, who sacrifice themselves for their young, or for companions of their own kind, and are sometimes capable of strictly monogamous unions, that in inferior animal nature the moral instinct becomes manifest and develops in proportion as the carnal instinct diminishes.