288 Dr Alison on the Principle of Vital Affinity, 



oxygen of the air, which appears to be the great agent in 

 the resolution of those compounds, which the vital affinities 

 have built up. 



6. On the other hand, the relation of starch and cellulose 

 to the lignin, which forms the greater part of the solid mat- 

 ters of dicotyledonous plants, seems to be nearly the reverse 

 of their relation to sugar. This matter is always found in- 

 crusting, or incorporated with, the cells of vegetable tex- 

 tures ; it gives them their solidity and strength, which all 

 decompositions by chemical agents impair ; it cannot be 

 formed from the compounds of starch by artificial means, 

 but is formed from them in greatest quantity when the vital 

 actions of plants are strongest ; and its composition is al- 

 ways stated as differing from the amylaceous compounds, by 

 containing more carbon, and less oxygen, in proportion to 

 the hydrogen, than exists in the composition of water; its 

 formula being stated as C40 H23 Ois. This, therefore, would 

 appear to be clearly the result of truly vital affinities, conti- 

 nuing to actuate the elements of starch, after the formation 

 of the starch from carbonic acid and water has been com- 

 pleted, and effecting a decomposition of part of the water, as 

 well as of the carbonic acid, presented to the living vege- 

 table. 



In studying this first and most striking of all the changes 

 which are to be ascribed to vital affinities, it is especially ne- 

 cessary to understand the parts assigned to carbon and oxy- 

 gen ; and, in taking this general view, we must regard vege- 

 tables and animals as inseparably linked together, and look 

 to the whole series of chemical changes which intervene be- 

 tween the origin of vegetables and the death and composition 

 of animals. We must regard the carbon, originally existing 

 in combination with oxygen in the atmosphere, in the pro- 

 portion of one equivalent to two, as the great 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. — [Gregory'' s Chemistry^ 

 p. 241.) That it may fulfil this office, it is invested with pe- 

 culiar but temporary powers ; it is separated at particular 

 points, and under certain conditions, from the oxygen, and 



