In the author's opinion, closing the mouth is a way of ensuring a better mood and overall state in life. His lively illustrations contrast a person whose mouth is often open - whether during sleep or waking hours - with an individual whose mouth is generally shut. Catlin's opinions were never accepted into the medical canon, but remain interesting in their historical context; Catlin was a painter and writer who spent years living among and painting members of various Native American tribes, gaining great admiration for their lifestyle and culture. Complimenting Catlin's other book on this subject - discusses more of the author's personal experiences and encounters. His respect and high regard for the Native Americans is evident as Catlin observes how many tribesmen and women keep their mouths closed. Even the mouths of Native American babies are closed by their mothers as they sleep; a practice Catlin believes helps the infant retain an even temper and serene appearance later in life.