VITAL PRINCIPLE. 33 



4. Atmospheric Air. If we suppose the existence of a 

 germ ready to expand, and furnished with a sufficient quan- 

 tity of moisture, and a suitable temperature, still, there is an- 

 other condition necessary to enable the living power to pro- 

 ceed to execute its functions, the presence of atmospheric 

 air. The decomposition of this fluid takes place wherever 

 there is living action. The portion of oxygen which it con- 

 tains disappears, and carbonic acid is substituted in its place. 

 These effects are produced by the seeds of plants, and the 

 eggs of animals. Nor is this decomposition confined to the 

 first stages of life : for we find the stems and leaves of plants, 

 the skin and lungs of animals, requiring a constant sup- 

 ply of air ; and, when this is withheld, decay and death 

 supervene. Judging from the most accurate experiments 

 which have been made on the subject, it appears to be de- 

 monstrated, that living bodies produce a superfluous quan- 

 tity of carbon, and that the presence of the oxygen gas of the 

 atmosphere is required to convert this into carbonic acid, for 

 the purpose of removing it more easily from the system. The 

 azotic gas in the atmosphere does not appear to exert any 

 positive influence on living bodies. It apparently serves 

 only to dilute the oxygenous portion. 



5. Nourishment. For the purpose of supplying mate- 

 rials for the increase of the structure, and the repair of the 

 waste which always results from living action, nourishment 

 is necessary for all organized bodies, and is sought after, 

 at stated periods, whenever the system is exercising its func- 

 tions. It is more or less fluid ; and differs both with regard 

 to its composition and quantity, according to the species. 



Life, then, requires the germ to have been detached 

 from a parent, supplied with moisture, excited by heat, and 

 furnished with air and food. 



III. Modifications of the Vital Principle. Having thus 

 attempted to ascertain the conditions necessary to the 

 VOL. I. c 



