115 



those organs ; and hence we see 1 , in all the forego- 

 ing examples, that the diminution in the volume of 

 expired air was greater in proportion as the respira- 

 tory organs suffered distress or oppression, and a- 

 mounted even to more than one-third of the air in- 

 spired when all voluntary powers ceased. 



93. By Mr Davy, however, and many others, the 

 difference in bulk between the volume of nitrous 

 oxide inspired, and that which is expired, is consi- 

 dered to arise in every case from a " rapid absorp- 

 tion of this elastic fluid by venal blood through the 

 moist coats of the pulmonary veins * :" and he also 

 thinks it " reasonable to suppose, that the whole 

 compound atmospheric air, passing through the 

 moist coats of the vessels, is first dissolved by the 

 serum of the venal blood, and, in its condensed 

 state, decomposed by the affinity of the red particles 

 for its oxygen ; the greater part of the nitrogen be- 

 ing liberated unaltered, but a minute portion of it 

 possibly remaining condensed in the serum and coa- 

 gulable lymph, and passing with them into the left 

 chamber of the heart f." It happens, rather unfor- 

 tunately for this opinion, that, in the natural respi- 

 ration of atmospheric air, a very small difference 

 exists between the inspired and expired volumes, 

 though the powers of absorption, if such there be, 

 must then be acting in their greatest vigour ; while 

 under an almost total exhaustion of muscular and 

 vital power, this absorption is considered to take 

 place in an extraordinary degree. But the subject 



* Researcher,, p. 396. Ibid. p. 4-47. 



H2 



