Plain Facts for Old and Young by John Harvey Kellogg

4. _Sudden change in disposition_ is a sign which may well arouse

suspicion. If a boy who has previously been cheerful, pleasant, dutiful, and gentle, suddenly becomes morose, cross, peevish, irritable, and disobedient, be sure that some foul influence is at work with him. When a girl, naturally joyous, happy, confiding, and amiable, becomes unaccountably gloomy, sad, fretful, dissatisfied, and unconfiding, be certain that a blight of no insignificant character is resting upon her. Make a careful study of the habits of such children; and if there is no sudden illness to account for the change in their character, it need not require long deliberation to arrive at the true cause, for it will rarely be found to be anything other than solitary indulgence.