568 



Miscellaneous. 



may admit of a chemical explanation ; at the same time, however, 

 we confess that our poor chemistry has not advanced so far as to be 

 able to imitate even this insignificant trifle, exactly in the same 

 manner as it occurs in the organised body. In sush a case, I think 

 the term ' vital force' would not be so very unsuitable to indicate all 

 that is still unknown to us. 



I'he author goes on speaking of the decomposition of carbonic acid 

 in leaves, and says (p. 123) that it has been proved by experiments 

 made with cut- off leaves, which of course did not receive any nitrogen 

 together with the carbonic acid, that nitrogen is not necessarily re- 

 quired for the decomposition of carbonic acid. Is this the art of mak- 

 ing experiments which is so much extolled, and can only be learnt in 

 chemical laboratories ? Does Dr. Liebig not know that every leaf itself 

 contains a great quantity of nitrogen, and that this matter is pos- 

 sessed of such qualities as enable it to produce the most astonishing 

 chemical metamorphoses and decompositions ? Is it possible that he 

 should be ignorant that every cut- off leaf, according to its nature, 

 sooner or later, ceases to decompose carbonic acid ? and what has he 

 to answer, when I inform him that it ceases to decompose carbonic 

 acid as soon as the nitrogen contained in it has been consumed. 

 Such propositions as the above are not admitted into vegetable phy- 

 siology. The author continues : " The carbon derived from carbo- 

 nic acid assumes a state in which it is soluble, and this we call 

 sugar, when it is sweet ; gum or mucus, when tasteless, and excre- 

 tions, when it is secreted by the roots, &c." Such observations as 

 these are as worthless in chemistry as in physiology. It is nonsense 

 to call sugar a fluid form of carbon, when oxygen and hydrogen are 

 as essential to its formation as carbon, and as it is only by the union 

 of these three substances that sugar is produced. Nor is there more 

 sense in what is said of excretions, among which occurs not only 

 matter containing nitrogen, but such varied substances as oil, resin, 

 oxalic acid, &c. 



The succeeding observations, which consist of aphorisms founded 

 on old facts, I might leave to the agriculturists, to whom they are 

 introduced, with the same courtesy as he has observed towards the 

 physiologists. I must, however, notice one passage, if only to prove 



