Plain Facts for Old and Young by John Harvey Kellogg

3. Begin the work of reform by purging the mind. If a lewd thought enters

the mind, dispel it at once. Cultivate a loathing for concupiscence. Never harbor such ideas for an instant, for they will surely lead to the overt act. If, perchance, the physical sin should not be committed, the thought itself is sin, and it leaves a physical as well as a moral scar almost as deep and hideous as that inflicted by the grosser crime.