179 



others, on the due circulation of the fluids of the 

 plant, and varying as that circulation varies. As we 

 observe this carbon, however, only in combination 

 with oxygen gas, its precise form or mode of exist- 

 ence cannot as yet be ascertained ; but the fact of 

 its always accompanying the exhalation of moisture 

 from the leaf, leads to the opinion, that it is not only 

 coincident with that excretion, but is carried on 

 likewise by the same structure ; the exhaled moisture, 

 as in the case of the seed, serving as the proper vehi- 

 cle of it* It appears also from the facts already stated 

 (134.), that carbon is afforded by the plant, as well 

 as by the seed, where no oxygen gas was present to 

 unite with it ; which shews that its emission depends 

 immediately on the power of the plant, and not on 

 any supposed chemical agency of the air. It may 

 be added, that the experiments of Dr Woodhouse 

 demonstrate likewise, that leaves as well as seeds, 

 under decomposition, form carbonic acid * : but this 

 we notice for the sake of discrimination only, since 

 we are now considering the changes which atmo- 

 spheric air undergoes from the agency of certain li- 

 ving processes alone. 



142. Ascending next, in the order of our inquiry, 

 into the animal kingdom, we find, that, to insects 

 and worms, the presence of oxygen gas is essential 

 to the continuance of living action (53. et seq.), 

 and that they gradually, and, in many instances, 

 completely convert this gas into carbonic acid. No 

 other substance but the animal being present in the 



* Nicholson's Journal, June 1802, p, 159. 

 M 2 



