136 Dr Alison on the Principle of Vital Affinity. 



the substance of tlie vegetable, — that under no other circum- 

 stances can water, carbonic acid, and ammonia, or their ele- 

 ments, be made to form these compounds, — and farther, that 

 after a time, when brought into contact, at the same tempera- 

 ture with the same vegetable substance in an ulterior stage 

 of its existence, they will form no such compounds, but will 

 aid and participate in the successive changes to w^hich vege- 

 table matter is liable after the phenomena of its living state 

 are over, and of which the ultimate result is, the resolution 

 of that matter into its original constituents. And from these 

 facts it seems quite reasonable to infer, that during the for- 

 mer, or what we call the living state of the vegetable, certain 

 affinities peculiar to the living state — i. e., certain vital affi- 

 nities — actuate the elements of which it is composed. 



In asserting the existence of vital affinities, we do not, in 

 the first instance, give any opinion whether it is by the addi- 

 tion of certain chemical attractions, or by the suspension of 

 others, during the living state, that the chemical changes pe- 

 culiar to that state are effected ; we assert nothing more than 

 what is, as I think, correctly stated in the following sentence 

 of Liebig : — " The chemical forces in living bodies are sub- 

 ject to the invisible cause by which the forms of organs are 

 produced." " The chemical forces are subordinate to this 

 cause of life, just as they are to electricity, heat, mechanical 

 motion, and friction. By the influence of the latter forces, 

 they suffer changes, in their direction, an increase or diminu- 

 tion of their intensity, or a complete cessation or reversal of their 

 action, 



" Such an influence, and no other, is exercised by the vital 

 principle over the chemical forces." 



" The equilibrium in the chemical attractions of the con- 

 stituents of the food is disturbed by the vital principle, as we 

 know it may be by many other causes. The union of its ele- 

 ments, so as to produce new combinations and forms, indicates 

 the presence of a peculiar mode of attraction, and the existence 

 of a power distinct from all other powers of nature, viz., the 

 vital principle." — {Organic Chemistry^ ^c, pp. 355, 357.) 



In these passages I think that Liebig has expressed him- 

 self with perfect accuracy ; but in other parts of his writings 



