356 RESPIRATION. 



elusions from, the particular fact, instead of the general 

 induction, which existing men sometimes call philo- 

 sophy in themselves and their contemporaries, but quite 

 another thing in those men that lived two hundred years 

 ago ; and it shows how careful even the most accurate 

 observers and the most sagacious reasoners should be, 

 that the statute with which they are going about to 

 augment the code of nature, does not run counter to 

 another, which is more general. Had they put the 

 question to the merest clown, whether the agents of 

 nature should be made fit to do their work before 

 doing it, or after, he would have had no difficulty in 

 pointing out the absurdity involved in the hypothesis 

 of imparting the oxygen to the blood of animals in any 

 other way than as an instrument for taking up some 

 matter which the blood had received in its circulation, 

 and which had become unfit for the purposes of life. 



The precise time that the oxygen may remain in 

 contact with the blood, and whether the whole, or only 

 part, and if any, what part of each inspiration is 

 given out again at the following expiration, is not 

 within the range of accurate experiment ; but we are 

 certain that the volume of expired air is very much the 

 same with that inspired, and that it comes out of the 

 lungs not deprived of the oxygen, but with oxygen, 

 (either its own or that of former inspirations,) com- 

 bined with a new substance, which is known in a sepa- 

 rate state only as a solid. That substance is carbon or 

 charcoal, which, when combined with oxygen, forms 

 carbonic acid ; the combination in which the oxygen 

 of air, that has been taken into and decomposed by the 

 respiratory organs of animals, is discharged from those 



