RESPIRATION 53 



rapidly with increase of body temperature, as in fever, and also 

 with physiological activity. Muscular activity greatly increases 

 oxygen consumption. Physiologists tell us that even shivering 

 multiplies the respiratory changes by two, and that external 

 cold has a similar effect. 



Parts. — The respiratory system consists of nasal chambers, 

 pharynx, larynx, trachea, bronchi, and lungs. These organs 

 are all lined with mucous membrane. This whole system is 

 merely a device to bring a thin sheet of blood into close rela- 

 tion with a sheet of air which has the needed oxygen. In other 

 words its function is to bring blood and air so near each other 

 that the exchange may be rapid and the blood take away oxygen 

 and leave waste matters. 



Nostrils. — Two in number. These are openings at the front 

 of the nasal cavities. The skin covering the nostrils is compara- 

 tively thin, quite sensitive, and supported by cartilages. 



The inferior turbinated bones, two in number, and scroll 

 shaped, are located on the outer wall of each nasal cavity. 

 Apparently they are there for the purpose of warming cold air 

 by their very rich blood supply and also provide a favorably 

 shaped, moist surface to catch dust and bacteria, on their way 

 to the lungs. 



Nasal cavities. — Two in number, one on each side of a median 

 partition. This partition is composed of the vomer, a portion 

 of the ethmoid, and the median cartilage. Each cavity connects 

 in front with the outside air through the nostril and behind with 

 the pharynx through an opening which may be called the pos- 

 terior nostril or, technically, the posterior nares. Each cham- 

 ber also connects laterally with the sinuses of the head (shown 

 in class). The floor, roof, and sides are formed by the various 

 face bones, together with portions of the frontal, ethmoid, and 

 sphenoid, and the median cartilage already mentioned. The 

 mucous membrane lining the nasal chambers is divided for study 

 into two portions: the upper, the olfactory, in which are dis- 

 tributed the terminations of the olfactory nerves, and the lower, 

 the Schneiderian. 



Pharynx. — This is a muscular sac situated beneath the 

 cranium, and back of the soft palate which constitutes a par- 

 tition between the pharynx and mouth cavities. This organ 

 belongs to both the respiratory and digestive systems. Its walls 

 are composed of two coats: the inner mucous and outer mus- 



