RESPIRATION 



271 



sumption of oxygen by the tissues affords an important 

 source of our bodily heat. And the main products of this 

 oxidation, water and carbon dioxide, are precisely those 

 which are formed by the burning of a candle or a stick 

 of wood. 



As the lungs are the principal organs from which the 

 blood gets its oxygen we may now consider their structure, 



s.c 



FIG. 199. Median section through nasal cavity, mouth and throat. 

 C, cavity of nose; E, opening of Eustachian tube from the ear; ep, epiglottis; 

 f,s, frontal sinus; g, glottis; hy, hyoid bone; j, lower jaw; /, larynx; oe, 

 esophagus; p', hard palate; p, soft palate ending posteriorly in the uvula, 

 u\ s.c, bones of spinal column; s.s, sphenoidal sinus; t, t, turbinated bones; 

 tl, tonsil; ton, tongue; tr. trachea; u, uvula. 



and see how they are adapted to the performance of their 

 functions. In order to enter the lungs the air has to flow 

 through a number of passages. First it is taken into the 

 nasal cavity where it is exposed to a wide surface of moist 

 mucous membrane. Here the air is not only warmed 

 before passing to the lungs, but dust and other particles 



