CHEMICAL CHANGES IN PLANTS AND ANIMALS. 349 



be gradually formed by replacement of more hydrogen, oxygen, 

 or other atoms by other residues. 



The following equations, while not showing the various 

 radicals and intermediate compounds formed, may illustrate 

 some of the results obtained by the plant in forming organic 

 compounds : 



C0 2 -f H 2 = H 2 CO 3 



H 2 CO.j O = H 2 CO 2 = Formic acid. 



2CO 2 + H 2 O = H 2 C 2 O 5 



H 2 C 2 O 3 O = H 2 C 2 O 4 = Oxalic acid. 



6CO 2 + 6H 2 O = C 6 H, a O 18 



C 6 H 1218 12 = C 6 H 126 = GluCOSe. 



10C0 2 + 8H 2 mm C 10 H 16 2g 



C io H i628 28 = C io H i6 = Oil of turpentine. 



10CO 2 + 4H 2 O + 2NH 3 = C 10 H 14 O 24 N 2 



C 10 H U O 24 N 2 24O = C 10 H 14 lSr 2 = Nicotine. 



The above formulas show that the formation of organic com- 

 pounds in the plant is alwa} 7 s accompanied by the liberation of 

 oxygen, and it may be stated as a general rule, that no organic 

 substance (produced in nature) contains a quantity of oxygen 

 sufficient to convert all carbon into carbon dioxide and all 

 hydrogen into water, which fact also explains the combustibility 

 of all organic substances. 



Why it is that the living plant has the power of forming 

 organic substances in the manner above indicated, we know 

 not, and we know very little even in regard to the means by 

 which the living cell accomplishes this formation, but we do 

 know that sunlight is that agent, the action of which is indis- 

 pensable for the plant in the formation of more complicated 

 organic substances from simpler ones. 



Decomposition of vegetable matter in the animal system. It has 

 been stated above, that the process of chemical decomposition 

 taking place in the animal system is chiefly regressive or destruc- 

 tive, that is to say : The substances formed in the plant are 

 taken into the animal system, where they are assimilated, and 

 then gradually oxidized by the inhaled atmospheric oxygen, 



