CHAPTER XXIV 

 RESPIRATION. THE GASEOUS INTERCHANGES 



Nature of the Problems. The study of the respiratory process 

 from a chemical standpoint has for its object to discover what are, 

 in kind and extent, the interchanges between the air in the lungs 

 and the blood in the pulmonary capillaries; and the nature and 

 amount of the corresponding gaseous changes between the living 

 tissues, and the blood in the systemic capillaries. Neglecting some 

 oxygen used up otherwise than in forming carbon dioxid, and some 

 carbon dioxid eliminated by other organs than the lungs, these 

 processes in the long run balance, the blood losing as much carbon 

 dioxid gas in the lungs as it gains elsewhere, and gaining as 

 much oxygen in the lungs as it loses in the systemic capillaries. 

 To comprehend the matter it is necessary to know the physical 

 and chemical conditions of these gases in the lungs, in the blood, 

 and in the tissues generally; for only so can we understand how 

 it is that in different localities of the Body such exactly contrary 

 processes occur. So far as the problems connected with the exter- 

 nal respiration are concerned our knowledge is tolerably complete ; 

 but as regards the internal respiration, taking place all through 

 the Body, much has yet to be learnt; we know that a muscle at 

 work gives more carbon dioxid to the blood than one at rest and 

 takes more oxygen from it, but how much of the one it gives and 

 of the other it takes is only known approximately; as are the con- 

 ditions under which this greater interchange during the activity 

 of the muscular tissue is effected: and concerning nearly all the 

 other tissues we know even less than about muscle. In fact, as 

 regards the Body as a whole, it is comparatively easy to find how 

 great its gaseous interchanges with the air are during work and. 

 rest, waking and sleeping, while fasting or digesting, and so on; 

 but when it comes to be decided what organs are concerned in 

 each case in producing the greater or less exchange, and how 

 much of the whole is due to each of them, the question is one far 

 more difficult to settle and still very far from completely answered. 



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