Comparative Physiology. 211 



and which do not serve for the support of the structure, until 

 united into new combinations (probably after being first de- 

 composed), we j)erceive the action of physical laws, operating 

 under those peculiar conditions which the living organism alone 

 can perfectly supply. Keasons have already been given for the 

 belief that the affinities which hold together the elements of 

 organised tissues are the same as those that prevail in the in- 

 organic world. We cannot yet succeed in producing artificially 

 any organic compound, even of the simplest kind ; but there 

 is no reasonable ground for doubt, that, if the elements could 

 be brought together in their requisite states and proportions, 

 the result would be the same as the natural compound. The 

 agency of vitality does not change the properties, but combines 

 them in modes which we cannot imitate. The operations in 

 vital chemistry are attended, like the changes in the composition 

 of inorganic substances, with a disturbance of electrical equili- 

 brium, and the late researches of Dr. Faraday have fully proved 

 the identity of electrical attraction with chemical affinity. Un- 

 less therefore a distinct set of laws could be established, regu- 

 lating vital affinities, we are scarcely justified in assuming that 

 these laws may not be accordant with those which we recognise 

 elsewhere." 



" In the changes denominated catalytic by Berzelius, a change 

 is produced by one body upon the composition of another, in- 

 dependent of any alteration or new combination of the first ; 

 while, in ordinary chemical combinations, change is effected by 

 the superior attraction of one agent, or of one of its elements, 

 for those of another. The peroxide of hydrogen, which is 

 readily decomj)osed by any substance having an affinity for oxy- 

 gen, is decomposed by metals, the fibrin of blood, &c. without 

 any change in themselves ; they produce in it a state analogous 

 to fermentation, oxygen escaping, and water being left. Most 

 metals at high temperatures, and platinum minutely divided at 

 low temperatures, produce the union of oxygen and hydrogen in 

 an explosive mixture. The action of sulphuric acid on alcohol, 

 in producing ether, without itself undergoing change, also the 

 conversion of gum or starch into sugar by the same agent, ap- 

 pear referable to the same class. . These substances exercise an 

 influence essentially distinct from what is known as chemical 

 affinity. Berzelius defines it as a new power, connected with 

 the electro-chemical." 



" The class of actions essentially vital are confined to, and 

 can only occur in, living organised structures ; they require 

 properties for their performance which are not to be met with 

 in other substances. Organisation is not confined to the solids 

 alone, for traces of it may be detected in the fluids by which 

 they are nourished. The blood in animals and the latex in 



p 4 



