OF THE RESPIRATION. 67 



vase filled with nitrogen or azote, a frog ; in this gas the frog 

 can live for a considerable time. Now analyze it, and you 

 will find that, although deprived of oxygen, the animal con- 

 tinues to give out carbonic acid gas. There can then be no 

 combustion, as Lavoisier supposed. 



124. In fact, the blood always contains carbonic acid 

 gas dissolved in it ; and Magnus has shown that the blood 

 can dissolve a certain measure of any gas with which it may 

 be brought in contact, by giving out a portion of the gas 

 first absorbed, when dissolving a portion of the second. 

 Thus, by shaking blood in hydrogen, a certain amount of gas 

 is absorbed, and a certain quantity of carbonic acid gas is set 

 free. The same happens when oxygen is used instead of 

 hydrogen, and the blood assumes an arterial character. 



125. It results, indeed, from numerous experiments, 

 that, as the changes observed to take place during respiration 

 equally happen to blood when contained in a bladder, oxygen 

 disappearing by being absorbed through the walls of the 

 bladder, and carbonic acid gas appearing, which must have 

 come from the blood and equally passed through the walls 

 of the bladder, the phenomena of respiration must in a 

 great measure be chemical, since they take place as well 

 in blood withdrawn from the body as in the pulmonary 

 vessels. 



126. What happens in the respiratory act seems to be 

 as follows : the venous blood coming from all parts of the 

 body reaches the lungs, holding in solution a considerable 

 amount of carbonic acid gas, a little azote, and some traces of 

 oxygen. As it passes through the lungs it comes as it were 

 in contact with the air, and dissolves a portion ; oxygen and 

 a certain amount of nitrogen are thus absorbed, and these 

 gases by being thus taken into the blood, expel a certain 

 amount of carbonic acid gas and of azote ; the carbonic acid 

 gas exhaled equals pretty nearly the amount of the oxygen 

 absorbed; the azote exhaled and absorbed are nearly equal, and 

 in addition there is the vapour or pulmonary transpiration. 

 Thus the blood loses carbonic acid gas, azote, and water, 

 whilst it becomes charged with oxygen and azote ; and thus 

 it may be proved, that arterial blood holds dissolved much 

 more oxygen than venous blood, and that it is to this gaseous 

 fluid that arterial blood owes its colour and qualities. Respi- 

 ration consists, then, in the phenomena of absorption and 

 exhalation, by means of which the venous blood, coming iu 

 F 2 



