NATURE OF ORGANIC CHEMICAL PROCESSES. 75 



bark of the willow (Piria). We are able to form 

 in our laboratories formic acid, oxalic acid, urea, 

 and the crystalline substances existing in the liquid 

 of the allantois of the cow, all products, it is said, 

 of the vital principle. We see, therefore, that this 

 mysterious principle has many relations in common 

 with chemical forces, and that the latter can indeed 

 replace it. What these relations are, it remains for 

 physiologists to investigate. Truly it would be ex- 

 traordinary if this vital principle, which uses every- 

 thing for its own purposes, had allotted no share 

 to chemical forces, which stand so freely at its dis- 

 posal. We shall obtain that which is obtainable 

 in a rational inquiry into nature, if we separate 

 the actions belonging to chemical powers from those 

 which are subordinate to other influences. But the 

 expression " vital principle " must in the mean time 

 be considered as of equal value with the terms 

 specific or dynamic in medicine : everything is specific 

 which we cannot explain, and dynamic is the ex- 

 planation of all which we do" not understand; the 

 terms having been invented merely for the purpose 

 of concealing ignorance by the application of learned 

 epithets. 



Transformations of existing compounds are con- 

 stantly taking place during the whole life of a 

 plant, in consequence of which, and as the results 

 of these transformations, there are produced gaseous 

 matters which are excreted by the leaves and blos- 

 soms, solid excrements deposited in the bark, and 

 fluid soluble substances which are eliminated by the 

 roots. Such secretions are most abundant imme- 

 diately before the formation and during the con- 

 tinuance of the blossoms ; they diminish after the 

 development of the fruit. Substances containing a 

 large proportion of carbon are excreted by the roots 

 and absorbed by the soil. Through the expulsion 

 of these matters unfitted for nutrition, the soil re- 

 ceives again with usury the carbon which it had at 



