Un été à la campagne (A Summer in the Countryside) was published in Paris in 1868, and is almost certainly by the novelist and journalist Gustave Droz (1832–95), though some think that the publisher Auguste Poulet-Malassis (1825–78) may have had a hand in its publication, if not in the writing.
Adèle and Albertine are adolescent school friends, looking forward to the summer holidays in the French countryside with their respective families; they are also thinking rather a lot about sex. The book is written as a series of forty-one letters, describing in detail how their experiences of intimacy develop over the long hot months.
In 1901 a private press English translation of Un été à la campagne was published in Paris, which you can read here, and an online French text can be found here.
Mercier’s stylish illustrations bring Un été à la campagne straight into the 1920s with slim young women and strong outlines.
Un été à la campagne was privately published in Paris (no publisher’s name is given) in a limited numbered edition of 280 copies.