286 MESSRS, ALLEN AND PEPYS ON THE RESPIRATION OF BIRDS. 



The production of carbonic acid in this case was somewhat greater than in 

 atmospheric air ; but the remarkable feature of this experiment is, that, except 

 in the formation of carbonic acid, the oxygen remains nearly unchanged, while 

 the whole loss falls upon the hydrogen ; so that the blood appears to have 

 absorbed a quantity of hydrogen, and given out a proportionate quantity of 

 azote, the total volume of gas before and after the experiment remaining nearly 

 the same. 



The present experiments tend to strengthen and confirm our former con- 

 clusions, and prove that when atmospheric air alone is respired in a natural 

 way, the proportion of azote is not altered, and that there is only a change of 

 a certain portion of oxygen for an equal portion of carbonic acid gas ; that 

 when a larger proportion of oxygen than is contained in atmospheric air is re- 

 spired, a quantity of oxygen is absorbed by the blood, and an equal quantity 

 of azote gas evolved. 



That when a mixture of hydrogen, oxygen, and azote are respired, the oxygen 

 being in the same proportion as in atmospheric air, there is no loss of oxygen, 

 but a quantity of hydrogen disappears and is replaced by the same quantity 

 of azote. 



The circulation of the blood is quicker in birds than in other animals ; and 

 if we may judge from the effects produced upon the pigeon, they are more 

 sensible to the stimulus of oxygen. 



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