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The next discovery of importance on respiration, is that by Dr. 

 Black, who observed the formation of carbonic acid. Succeeding la- 

 bourers in the same field of inquiry, it is observed, are too numerous 

 for justice to be done to every one ; and the principal information 

 collected from them relates to measures of quantity. Dr. Goodwin 

 estimated the residual gas in the lungs, after expiration, at 109 inches. 

 Dr. Menzies found the absorption of oxygen nearly 52,000 inches in 

 twenty-four hours. 



Lavoisier and Seguin, from a series of elaborate experiments, con- 

 cluded that more oxygen was absorbed than evolved, as carbonic acid, 

 and thence imagined that water was formed by the union of oxygen 

 and hydrogen in the lungs. 



Their experiments showed the consumption of oxygen to be greater 

 in a colder atmosphere, and to be increased also during digestion 

 and during exercise ; and they estimated the average consumption at 

 41,000 inches per day. 



The quantity of carbonic acid formed, was first estimated by Mr. 

 Davy. 



The authors conceiving that many important points are not yet 

 satisfactorily settled, undertake to examine in the present communi- 

 cation, 



1 . The average quantity of oxygen converted into carbonic acid in 

 ordinary respiration. 



2. Whether oxygen is absorbed by the blood. 



3. Whether azote is absorbed, and whether hydrogen or other gas 

 is evolved. 



On account of the impossibility of knowing, with precision, the 

 quantity of gas remaining in the lungs after expiration, and the con- 

 sequent difiiculty of deciding whether any gas is absorbed in the act 

 of respiration, it was determined to perform the experiments on such 

 large quantities of air at a time, that the error arising from residual 

 gas might bear a small proportion to the whole quantity. 



The apparatus for the first five experiments consisted of two ga- 

 someters, one of which contained 4200 inches of atmospheric air over 

 water, from which the inspirations were made, and the other being 

 filled with mercury, was employed to receive the gas after expiration; 

 but as its capacity was only 300 inches, it was necessary for the 

 operator to retain his breath for about fifteen or twenty seconds, till 

 the quantity expired had been read off, noted, and expelled from the 

 gasometer ; after which the same process was repeated about twelve 

 times. The quantity of inspired air having now been read off from 

 the water gasometer, the quantity expired was ascertained by casting 

 up the amount of the successive fillings of the mercurial gasometer. 

 From an average of these five experiments, there appeared to be a 

 diminution of twenty inches in 3700. But the authors are inclined 

 to ascribe this difference to the difiiculty above mentioned, of bring- 

 ing the lungs to the same state of contraction after the experiment 

 as they had been before. 



In determining the quality of the expired gas, lime-water was first 



