This is because it is the job of the nose to filter out all of the particles that enter the body, as well as to humidify the air we breathe, add moisture to it, and warm it to body temperature. In addition, nasal breathing produces nitric oxide within the body while mouth breathing does not. Mouth breathing also leads to dry mouth, throat infections, a reduced sense of taste, and other chronic conditions. Nasal breathing is a research interest in Orthodontics (and the related field of Myofunctional Therapy) and for biological anthropologists. Infants Human infants are commonly described as obligate nasal breathers as they breathe through their nose rather than the mouth. Most infants, however, are able to breathe through their mouth if their nose is blocked. There are however certain infants with conditions such as choanal atresia in which deaths have resulted from nasal obstruction. In these cases there are cyclical periods of cyanosis. The infant initially attempts to breathe through the nose, and is unable to; hypercapnia occurs, and many babies instinctively begin to cry. While crying, oral ventilation occurs and cyanosis subsides. There is variation in the length of time until a baby begins oral breathing, and some will never cease attempts at nasal breathing. It has also been suggested that infants may not be able to sustain oral breathing for significant lengths of time, because of the weakness of the muscles required to seal the nasal airway and open the oral airway. One study employing monitored anatomical occlusion concluded that human infants are not obligate nasal breathers: its sample of nineteen infants, ranging in age from 1 day to 7.5 months, reliably transitioned from nose to mouth breathing after nasal occlusion, providing evidence that infants possess the physiological capability to mouth breathe. Exercise Some authors argue that nasal breathing offers a greater advantage over mouth breathing during exercise. Additional people and activities George Catlin George Catlin was a 19th-century American painter, author, and traveler, who specialized in portraits of Native Americans in the Old West. Travelling to the American West five times during the 1830s, he wrote about the life of the Plains Indians, and painted portraits that depicted them. He was also the author of several books, including The Breath of Life (later retitled as Shut Your Mouth and Save Your Life) in 1862. It was based on his experiences traveling through the West, where