12 OXYGEN REQUIRED 



At every moment of his life man is taking oxygen 

 into his system, by means of the organs of respiration ; 

 no pause is observable while life continues. 



The observations of physiologists have shown, that 

 the body of an adult man, supplied with sufficient food, 

 has neither increased nor diminished in weight at the 

 end of twenty-four hours ; yet the quantity of oxygen 

 taken into the system during this period is very consid- 

 erable. 



According to the experiments of Lavoisier, an adult 

 man takes into his system, from the atmosphere, in one 

 year, 746 Ibs., according to Menzies, 837 Ibs. of oxy- 

 gen ; yet we find his weight, at the beginning and end 

 of the year, either quite the same, or differing, one way 

 or the other, by at most a few pounds, (i)* 



What, it may be asked, has become of the enormous 

 weight of oxygen thus introduced, in the course of a 

 year, into the human system ? 



This question may be answered satisfactorily : no 

 part of this oxygen remains in the system ; but it is 

 given out again in the form of a compound of carbon or 

 of hydrogen. 



The carbon and hydrogen of certain parts of the 

 body have entered into combination with the oxygen 

 introduced through the lungs and through the skin, and 

 have been given out in the forms of carbonic acid gas 

 and the vapor of water. 



At every moment, with every expiration, certain 

 quantities of its elements separate from the animal or- 



* The Numbers refer to the Appendix. 



