RESPIRATION. 359 



respiration, in contradistinction to the thoracic movements by which 

 the air is brought into relation with the blood, and which 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 

 chemic changes which are related to the exchange of gases between 

 the air in the lungs and the blood, on the one hand, and between 

 the blood and tissues, on the other. 



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 constitutes 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 understanding of the phenom- 

 ena 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. f Oxygen, 16.02. 



100 I Carbon dioxid,, traces. 100 | Carbon dioxid, 4.38. 



vols. 1 Nitrogen, 79.20. vols. 4 Nitrogen, 79.60. 



t Watery vapor, variable. | Watery vapor, saturated. 



( Organic matter. 



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 analysis of gases. Their construction as well as the methods 



