338 THE CHEMISTRY OF CREATION. 



brought prominently under our view. 1st. 

 There is a discharge of carbonic acid gas from 

 the lungs. 2nd. In the lungs, a remarkable 

 alteration takes place in the blood. And we 

 must proceed immediately to add to them 

 a third, of nearly equal importance; namely, 

 That while carbonic acid gas is discharged from 

 the lungs, a quantity of the oxygen of the in- 

 spired air is received by them, and disappears 

 in the process of respiration. Thus, to put the 

 changes in clear terms, from the measure of air 

 which goes into the lungs, a certain measure of 

 oxygen is abstracted, the place of which is 

 supplied by the addition of carbonic acid. We 

 are naturally, therefore, led to suppose that 

 these three chemical phenomena the change 

 of the blood, the absorption of oxygen, and the 

 discharge of carbonic acid gas in respiration 

 are in some measure connected with each other. 

 Their connexion is as follows : 



The blood in circulating along the arteries, 



GO * 



through the fine capillary vessels, to the veins 

 which carry it back to the heart, and in the per- 

 formance of its various duties, as the source of 

 nutrient and regenerative matter, to every por- 

 tion of the animal frame besides parting with 

 many other ingredients, loses a large amount of 

 oxygen which, in its condition as arterial blood, 

 it had previously contained. In so doing, it 



