CHAPTER VIII 

 RESPIRATION 



' 242. Nature and Object of Respiration. The blood, as 

 we have learned, not only provides material for the growth 

 and activity of all the tissues of the body, but also serves 

 as a means of removing from them certain waste products. 



We have now to consider a new source of nourishment 

 to the blood, viz., that which it receives from the oxygen 

 of the air. We are also to learn one of the methods by 

 which the blood gets rid of poisonous waste matters. 



We are to study the process of respiration, or the means 

 by which oxygen is supplied to the various tissues, and by which 

 the principal waste matters, or chief products of oxidation, are 

 removed from the tissues. 



243. The Respiration of the Tissues. The tissues are 

 continually taking in oxygen and are continually producing 

 carbon dioxide and other waste products. In fact, the life 

 of the tissues is dependent upon a continual succession of 

 oxidations. When the blood leaves the tissues it is poorer 

 in oxygen, and is richer in carbon .dioxide. This exchange 

 of gases between the blood and the tissues is sometimes 

 spoken of as the respiration of the tissues, or internal respiration. 



244. The Essential Step in Respiration. Now, as we 

 have seen, the capillaries of the lungs are the only means 

 of communication between the pulmonary arteries and the 

 pulmonary veins. The blood in the pulmonary capillaries 

 is separated from the air only by a delicate tissue formed 



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