RESPIRATION 413 



from the tissues to the lungs. The respiratory movements constitute the 

 means by which the oxygen of the air is brought into, and the carbon dioxid 

 expelled from, the lungs into the surrounding air. 



The exchanges between the blood and the tissues constitute internal 

 respiration, while the exchanges between the blood, the intra-pulmonic and 

 the atmospheric air, the result of the mechanic movements of the thorax, 

 constitute external respiration. The transfer of the oxygen by the blood 

 from the interior of the lungs to the tissues, and of the carbon dioxid from 

 the tissues to the interior of the lungs, is the outcome of a series of physical 

 and chemic changes which are related to the exchange of gases between the 

 air in the lungs and the blood, on the one hand, and the exchange of gases 

 between the blood and tissues, on the other hand. 



In consequence of the many and complex chemic changes which attend 

 these gaseous exchanges, there arise changes in composition of: 



1. The air breathed. 



2. The blood, both arterial and venous. 



3. The tissue elements and the lymph by which they are surrounded. 



The investigation of the nature of these changes, the mechanism of their 

 production, and their quantitative relations constitute the subject-matter of 

 the chemistry of respiration. 



CHANGES IN THE COMPOSITION OF THE AIR 



Experience teaches that the air during its sojourn in the lungs undergoes 

 such a change in composition that it is rendered unfit for further breathing. 

 Chemic analysis has shown that this change involves a loss of oxygen, a gain 

 in carbon dioxid, watery vapor, and organic matter. For the correct under- 

 standing of the phenomena of respiration it is essential that not only the 

 character but the extent of these changes be known. This necessitates an 

 analysis of both the inspired and expired airs, from a comparison of which 

 certain deductions can be made. 



The results which have been obtained are represented in the following 

 table: 



Inspired Air. Expired Air. 



f Oxygen 20 . 80. 

 Carbon dioxid traces. 



vols. J Nitrogen 79 .20. 



100 

 vols. 



Oxygen 16.02. 



Carbon dioxid . . 4 . 38. 



Nitrogen 79 .60. 



Watery vapor. . saturated. 



( Watery vapor variable. 



Organic matter . a trace. 



These analyses indicate that under ordinary conditions the air loses 

 oxygen to the extent of 4.78 per cent, and gains carbon dioxid to the extent 

 of 4.38 per cent. ; that it gains in nitrogen to the extent of 0.4 per cent, and in 

 watery vapor from its initial amount to the point of saturation, as well as in 

 organic matter. It is to these changes in their totality that those disturbances 

 of physiologic activity are to be attributed which arise when expired air is 

 re-breathed for any length of time without having undergone renovation. 



Special forms of apparatus have been devised for the collection and analy- 

 sis of gases. Their construction as well as the methods of analysis involved 

 are complicated and need not be described in this connection. ' The presence 

 of the carbon dioxid, however, may be readily shown by breathing through 

 a glass tube into a vessel containing barium or calcium hydrate solution. The 



