Liehig's Organic Chemistry applied to Agriculture, 559 



fermentation. That the microscope may lead to more certain 

 results than common chemistry, may be proved by his view of the 

 composition of starch ; and v^^hat he says of gluten in bread (p. 36), 

 proves nothing more than that he does not know how to use a mi- 

 croscope. Nobody has ever thought of distinguishing, either with 

 the microscope or the naked eye (for in this matter it is the same), 

 things which possess the same qualities in an optical view. But if, 

 as is probable, gluten and dextrin have a different capacity of refract- 

 ing light, and these two substances are indeed mechanically mixed 

 up in the bread. Dr. Liebig may be certain that the distribution of 

 gluten in bread may be discovered as well by the microscope as by 

 his chemical processes. 



As to the inability of physiologists to make experiments, I confess 

 that we do not make experiments like those of Dr. Liebig, where a 

 fish-pond represents the pneumatic trough, and a skating- ground a 

 graduated tube. They know too well what they are about, and that 

 their object is not to reason about the possibility of a chemical or 

 physical explanation, but to ascertain how nature proceeds in her 

 operations in each given case. We are far indeed from being able 

 to effect this, and the principal reason of our inability must be looked 

 for in the state of chemistry, which leaves us in the lurch, and 

 offers nothing to our assistance except a great number of ines and 

 ides, which are useless in the explanation of the theory of vital ac- 

 tions ; and about as many hypotheses respecting the composition of 

 organic matter, which are just as useless, because they do not rest 

 on consistent ideas and are not coherent in themselves. Dr. Liebig 

 is, no doubt, able to explain how, according to the opinion of some 

 chemists, it may be imagined that an atom of starch is composed by 

 the combination of his elements ; but can he prove how it must be 

 composed according to scientific principles, which do not admit of 

 any objection ? Is Dr. Liebig able to give us a theory which ex- 

 plains the transformation of starch into gum and sugar, &c., and 

 which contains something more than empty phrases — such as catalys, 

 contact, a body in activity, and so forth ? So long as in these two 

 matters, which themselves constitute the real foundation of vege- 

 tation, we cannot give a satisfactory explanation, we can hardly 

 expect to understand the zoochemistry of the cells of plants ; never- 



4 B 



