XXVII. RESPIRATION AND EXCRETION 



Problem LI. A study of the organs and process of respiro/- 

 tion. {Laboratory Manual, Proh. LI.) 

 (.a) Organs of respiration in frog. 

 (J)) Meclianirs of respiration. 

 (c) Process of respiration in the lungs. 



Necessity for Respiration. — We have seen that plants and ani- 

 mals need oxygen in order that the life processes may go on. Food 

 is oxidized to release energy, just as coal is burned to give heat 

 to run an engine. As a draft of air is required to make fire under 

 the boiler, so, in the human body, oxygen must be given so that 

 foods or tissues may be oxidized to release energy used in growth. 

 This oxidation takes place in the cells of the body, be they part of a 

 muscle, a gland, or the brain, f Blood, in its circulation to all -parts 



of the body, is the medium 

 which conveys the oxygen to 

 that -place in the body where 

 it will be used. ' 



The Organs of Respira- 

 tion in Man. — We have 

 alluded to the fact that 

 the lungs are the organs 

 which give oxygen to the 

 blood and take from it 

 carbon dioxide. The 

 course of air passing from 

 the outside of the lungs in 

 man is much the same as 

 in the frog. Air passes 



Air passages in the human lungs: a, larynx ; h, 

 trachea (or windpipe) ; c, d, bronchi ; e, bron- 

 chial tubes ; /, cluster of air cells. 



through the nares, the 

 glottis, and into the windpipe. This cartilaginous tube, the top 

 of which may easily be felt as the Adam's apple of the throat, 



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