138 Dr Alison on the Principle of Vital Affinity. 



table and animal, is still essentially dependent ; and because 

 the simplicity of the process makes it a fit case for consider- 

 ing the question, whether the power here named is strictly 

 entitled to the epithet vital ; or whether, as some eminent 

 physiologists in this country maintained, the idea expressed 

 by that term is incorrect and unscientific. 



The opinion of those who oppose the doctrine of vital affi- 

 nity, is thus distinctly stated in the Anatomy of Drs Quain 

 and Sharpey : 



" Although the products of chemical changes in living 

 bodies for the most part diff'er from those appearing in the 

 inorganic world, the difference is nevertheless to be ascribed, 

 not to a peculiar or exclusively vital affinity diff'erent from 

 ordinary chemical affinity, but to common chemical affinity, 

 operating in circumstances or conditions which present them- 

 selves in living bodies only ; and undoubtedly, the progress 

 of chemistry is daily adding to the probability of this view." 



I consider this to be a hasty and ill advised statement ; 

 and to shew this, I request attention, y?r*/, to the perfect sim- 

 plicity of the apparatus by which this change is eff'ected. 

 " In all plants,'^ says Mulder, " there exists a small organ, 

 of the most simple form, although employed by nature for 

 the most varied purposes. It is a small filmy sac, a thin 

 membrane, which encloses a small space, which it enables to 

 communicate with the exterior space through invisible pores. 

 These little sacs or cells are the chief organs of plants. A 

 countless multitude of them, grouped together, forms the 

 whole bulk of the plant, so that if every thing except the 

 cells be destroyed, the shape and size of the plant are not in 

 the least changed or diminished." 



Into this simple apparatus in certain parts of plants, water, 

 impregnated with carbonic acid, is introduced, while the 

 plants exhibit the phenomena of life ; and let us next observe 

 the intensity of the action by which the carbonic acid is there 

 decomposed, the carbon attached to the elements of the wa- 

 ter, and the oxygen set free. " This is done by a power," 

 says Liebig, " to which the strongest chemical action cannot 

 be compared. The best idea of it may be formed by consi- 

 dering, that it surpasses in power the strongest galvanic bat- 



