178 APPLIED PHYSIOLOGY 



this way as much as 2 quarts of water in the twenty- 

 four hours. It is warmed by passing over the highly 

 vascular mucous membrane, the surface of which is 

 increased by the projection of the turbinates, just as the 

 surface of a radiator by which one warms a room is 

 multiplied by its projecting metal bars. How efficiently 

 the warming is carried out may be judged from the 

 result of experiments, which show that air entering the 

 nose at the freezing-point is warmed to a temperature of 

 81 F. by its passage through the nose alone. 



But the nerves of the nose have also a protecting part 

 to play. The sense of smell is no doubt primarily 

 protective rather than aesthetic. It warns us of the 

 presence of gases which might be injurious to the lungs. 

 Nor is the common sensibility of the nose without its 

 uses. Stimulation of the branches of the fifth nerve in 

 the nasal mucous membrane has been found to induce a 

 reflex contraction of the bronchial muscles,* and so 

 prevent the entrance of air into the lungs. It can easily 

 be understood that in many circumstances as, for 

 example, when irritating fumes have been inadvertently 

 inhaled this may be a real source of protection to the 

 lungs, t Sometimes, on the other hand, this reflex 

 mechanism becomes unduly sensitive, and brings about 

 spasm of the bronchial muscles on quite inadequate 

 provocation, and it is in this way that some cases of 

 asthma are caused. 



* See Dixon and Brodie, Journ. of Physiol., 1903, xxix. 97, 

 and Trans, of the Path. Soc. of London 1903, liv. 17. 



f See Mackenzie, Amer. Journ. of Med. Sciences, 1883, Ixxxvi., 

 106; also Riegel and Edinger, Zeit.f. Klin. Med., 1882, v. 413. 



