PART IV 

 RESPIRATION, VOICE AND SPEECH 



SECTION XII 

 RESPIRATION 



I 



CHAPTER XXXVI 



THE STRUCTURE AND FUNCTION OF THE ELEMENTARY 



LUNG 



Introduction. — In its widest sense the term respiration is applied 

 to the interchange of the gases between hving substance and the 

 medium in which it is contained. This is true of animals as well as of 

 plants, and since by far the greatest number of protoplasmic entities 

 take up oxygen and give off carbon dioxid, respiration is practically 

 restricted to the acquisition of the former gas and the discharge of 

 the latter. Oxygen is also taken into the body in Other ways, for 

 example, as a constituent of the food, but it is practically impossible 

 for the cells to make use of it in this form. This implies that the cells 

 do not possess the power of separating it from its combinations and 

 hence, it is evident that this gas must be presented to them in an easily 

 assimilated form, namely, as ''respiratory oxygen." 



It is commonly held that animals inhale oxygen and exhale carbon 

 dioxid, while plants inhale carbon dioxid and exhale oxygen. In this 

 way, it is assumed, a continuoiis equilibrium of these gases is had for 

 all time to come. As a matter of fact, however, plants possess the 

 same respiratory interchange as animals, oxygen being inspired by 

 them and carbon dioxid expired. Nevertheless, it is true that plants, 

 when exposed to sunlight, liberate oxygen, but this excess of the gas 

 does not find its origin in a respiratory activity but in an increased 

 metabohsm which is associated with the assimilation of the starches. 



If we regard the bacteria as members of the animal kingdom, 

 a classification which is not at all uncommon at the present time, 

 it may be said that animals are either aerobic or anaerobic. This 

 designation is intended to convey the idea that some of them thrive 



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