Ellis claims that sexual self-excitement is known to happen at an early age. He references authors like Marc, Fonssagrives, and Perez in France who published their findings in the nineteenth century. These early ages are not strictly limited to ages close to puberty as can be seen in their findings. These authors provide cases for children of both sexes who have masturbated from the age of three or four. Ellis references Robie's findings that boys’ first sex feelings appear between the ages of five and fourteen. For girls, this age ranges from eight to nineteen. For both sexes, these first sexual experiences arise more frequently during the later years as opposed to the earlier years. Ellis then references G.V. Hamilton’s studies that found twenty percent of males and fourteen percent of females have pleasurable experiences with their sex organs before the age of six. This is only supplemented by Ellis’ reference to Katharine Davis’ studies, which found that twenty to twenty-nine percent of boys and forty-nine to fifty-one percent of girls were masturbating by the age of eleven. However, in the next three years after, boys’ percentages exceeded those of girls. Ellis also contributed to the idea of varying levels of sexual excitation. He asserts it is a mistake to assume all children are able to experience genital arousal or pleasurable erotic sensations. He proposes cases where an innocent child is led to believe that stimulation of the genitalia will result in a pleasurable erection. Some of these children may fail and not be able to experience this either pleasure or an erection until puberty. Ellis concludes, then, that children are capable of a "wide range of genital and sexual aptitude". Ellis even considers ancestry as contributions to different sexual excitation levels, stating that children of "more unsound heredity" and/or hypersexual parents are "more precociously excitable". Ellis' views of auto-eroticism were very comprehensive, including much more than masturbation. Auto-eroticism, according to Ellis, includes a wide range of phenomena. Ellis states in his 1897 book "Studies in the Psychology of Sex", that auto-eroticism ranges from erotic day-dreams, marked by a passivity shown by the subject, to "unshamed efforts at sexual self-manipulation witnessed among the insane". Ellis also argues that auto-erotic impulses can be heightened by bodily processes like menstrual flow. During this time, he says, women, who would otherwise not feel a strong propensity for auto-eroticism, increase their masturbation patterns.