163 



quantity of air which the cavity contained will be 

 equal to 105 cubic feet. If we suppose this air to 

 have been at first similar in composition to that of 

 the atmosphere, containing ^ of oxygen gas, the 

 quantity of that gas may be taken at 23 cubic feet, 

 by which the function of respiration was supported 

 for more than seven days. But, in ordinary respira- 

 tion, the daily consumption of oxygen ( 1 22. ) a ounts 

 to 26 cubic feet ; so that, in this case, animal life was 

 protracted for seven days on much less than one-se- 

 venth of the usual quantity of that gas. When, 

 however, death does happen to animals confined in 

 a given volume of air, it must arise either from the 

 noxious operation of the nitrogen gas that is always 

 present, or from that of the carbonic acid, which is 

 formed ; or it must proceed from the deficiency, or 

 total absence, of oxygen gas. Now, although nitro- 

 gen gas do not of itself support life, yet we have 

 no evidence that it exerts any injurious effect on the 

 animal system. In vegetation (5. 29.), and in the 

 respiration of the inferior animals (73.), it has been 

 shewn to be wholly inactive ; and when, in the ex- 

 periment of Lavoisier (127.)> it constituted || of 

 the air employed, a degree of drowsiness only seems 

 to have been induced by it. That it is entirely pas- 

 sive, is still farther confirmed by an experiment of 

 Lavoisier, who found that hydrogen gas, mixed in 

 due proportion with oxygen, would serve the pur- 

 poses of respiration as well as the air of the atmo- 

 sphere. We have no proof that nitrogen is able to 

 enter the vessels so as to produce any direct opera- 

 tion on the blood, an effect which is still farther 



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