CONDITIONS ESSENTIAL TO NUTRITION. 61 



nor air, nor oxygen, is fitted to support life ? Cer- 

 tainly not. 



From the pedestal of the Trajan column at Rome 

 we might chisel out each single piece of stone, if 

 upon the extraction of the second we replaced the 

 first. But could we conclude from this that the col- 

 umn was suspended in the air, and not supported by 

 a single piece of its foundation ? Assuredly not. 

 Yet the strongest proof would have been given that 

 each portion of the pedestal could be removed, with- 

 out the downfall of the column. 



Animal and vegetable physiologists, however, come 

 to such conclusions with respect to the process of 

 assimilation. They institute experiments, without 

 being acquainted with the circumstances necessary 

 for the continuance of life, — with the qualities and 

 proper nutriment of the animal or plant on which 

 they operate, — or with the nature and chemical con- 

 stitution of its organs. These experiments are con- 

 sidered by them as convincing proofs, whilst they 

 are fitted only to awaken pity. 



Is it possible to bring a plant to maturity by means 

 of carbonic acid and water, without the aid of some 

 substance containing nitrogen, which is an essential 

 constituent of the sap, and indispensable for its pro- 

 duction ? Must the plant not die, however abundant 

 the supply of carbonic acid may be, as soon as the 

 first small leaves have exhausted the nitrogen con- 

 tained in the seeds ? 



Can a plant be expected to grow in Carrara mar- 

 ble, even when an azotized substance is supplied to 

 it, if the marble be sprinkled with an aqueous solu- 

 tion of carbonic acid, which dissolves the lime and 

 forms bicarbonate of lime ? A plant of the family of 

 the PlumbaginecB, upon the leaves of which fine 

 hornlike, or scaly processes of crystallized carbonate 

 of lime are formed, might perhaps attain maturity 

 under such circumstances ; but these experiments 

 are only sufficient to prove, that cresses, gourds, and 

 balsamines, cannot be nourished by bicarbonate of 



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