THE PRINCIPLE OF VITAL AFFINITY. 187 



starch from carbonic acid and water has been completed, and effecting a decom- 

 position of part of the water, as well as of the carbonic acid, presented to the 

 living vegetable. 



In studying this fii'st and most striking of all the changes which are to be 

 ascribed to vital affinities, it is especially necessary to understand the parts as- 

 signed to Carbon and Oxygen ; and, in taldng this general view, we must regard 

 vegetables and animals as inseparably linked together, and look to the whole 

 series of chemical changes which intervene between the origin of vegetables and 

 the death and decomposition of animals. We must regard the carbon, originally 

 existing in combination with oxygen in the atmosphere, in the proportion of one 

 equivalent to two, as the gi-eat agent employed by Nature in the formation of the 

 whole organized creation, insomuch that all organic chemistry may be said to be 

 the chemistry of compounds of carbon. — {Gh'egory''s Chemistry, p. 241.) That it 

 may fulfil this office it is invested with peculiar but temporary powers ; it is se- 

 parated at particular points and under certain conditions from the oxygen, and 

 attaches itself to the elements of water, always present where vegetables grow, 

 and so forms various compounds, beginning with the varieties of starch ; in all 

 which it is the principal ingredient. The compounds thus formed next attack and 

 partially decompose the water and appropriate the hydrogen, thus causing a far- 

 ther evolution of oxygen, and forming oil ; and afterwards nitrogen, in small quan- 

 tity, is introduced, and fresh transformations take place, by which the protein 

 compounds are formed. All the solid structures of vegetables, and indeed of 

 organized beings generally, are made up of these compounds of carbon, in which 

 oxygen exists either in the proportion to hydrogen which forms water, or in a 

 less proportion than that ; and the formation of these may be confidently ascribed 

 to vital affinities. But it is easy to conceive that other compounds of carbon with 

 hydrogen and oxygen will exist in plants in which the oxygen will be in larger 

 proportion than this, without supposing ox3^gen from the air to be added ; because 

 the vital affinities may not have been in sufficient force to separate the oxygen 

 completely from its original union with carbon, and these, therefore, may be re- 

 garded as compounds of carbon, water, and undecomposed carbonic acid. Such 

 are the different organic acids (the citric 12C 8H 14 0=9 C + 8 HO + 3 COo, the 

 malic 8C 6H 10 0=6 C + 6 HO + 2 CO., the tartaric 8C 4H 10O=5C + 4HO 

 + 3 CO,, the oxalic 4C2H80=C + 2HO-h3 CO,,) which are found in the juices 

 of many vegetables, particularly in the immature state. 



Again, it is always to be observed, not only that all organized bodies are 

 destined ultimately to revert to the water, carbonic acid, and ammonia, from 

 which they were originally formed, but that, in the case of animals at least, there 

 is a process always going on during the state of life, by which these same inor- 

 ganic matters are continually evolved from the living frames. Therefore, we 

 cannot be surprised to find that the fluids of aU living animal bodies contain othe)- 



