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CHAPTER XXXIII 
RESPIRATION AND EXCRETION 
In this chapter are combined the two fundamental life 
processes of respiration and excretion together with a descrip¬ 
tion of the more important organs 
that are necessary to the per¬ 
formance of these processes. Two 
important practical problems are 
suggested as a result of a discus¬ 
sion of these topics. The problem 
of leather naturally follows the 
description of the skin and the 
problem of sewage follows the 
general subject of excretion. 
353. Respiration is the life pro¬ 
cess in which oxygen is used in 
the cells of 
the bodies of 
plants and 
animals, and carbon dioxide eliminated 
from them. All animals carry on respira¬ 
tion, and in all the process is alike, al¬ 
though the various animals use different 
structures to secure the interchange of 
oxygen and carbon dioxide. The hydra 
plain their work. an d ear thworm use the entire surface of 
the body in this process; the fish has special organs, the 
gills, while the frog and man have lungs. 
443 
Figure 392. — The Lungs and 
Heart. 
Note the branches of the 
bronchus and blood vessels on 
the right side. 
Figure 393. — Cili¬ 
ated Epithelium. 
Such cells line our 
bronchial tubes. Ex- 
