Liebig's Organic Chemistry applied to Agriculture. 563 



such operations by a better terra. Both in organic changes and in 

 the chemical processes of assimilation, superficial people deceive 

 themselves, when they fancy they have succeeded in imitating such 

 processes in their crucibles. Let us suppose that starch is converted 

 into sugar in a germinating plant, in the same way as in a mash-tub ; 

 can you, Dr. Liebig, explain the process of fermentation, or do you 

 know anything about the transforming power of yeast, or sulphuric 

 acid Call such phenomena, then, vital force, specific, dynamic ; 

 and be content with terms which you reject with such chemical 

 indignation. We physiologists employ these terms to express phe- 

 nomena which we cannot explain ; and we do not attempt to pass off 

 our ignorance for wisdom, as the chemist does with his catalyse, 

 contra-action, and bodies in activity. But enough. Pursuing the 

 proper subject of this chapter, we find the old observation, that 

 humus contributes to the nourishment of the plants by forming car- 

 bonic acid, and then another instance of the carelessness with which 

 Dr. Liebig has formed his notions. He says, charcoal can be used 

 as a complete substitute for mould, for it never forms carbonic acid. 

 I have little doubt that Dr. Liebig, when he was writing this, had 

 in his head the idea that humus condenses carbonic acid from the at- 

 mosphere, and thus introduces it into plants, and that in this impor- 

 tant quality, which, however, he entirely omits, humus and charcoal 

 agree. This fact, however, we do not learn from Dr. Liebig, but 

 from Lucas, Berzelius, and Mitscherlich. 



In the succeeding chapter, in treating of " the assimilation of 

 hydrogen," Dr. Liebig thinks it much more probable that water is 

 decomposed, than carbonic acid, though previously (p. 18.) he had 

 declared that the latter was a fact beyond all doubt. In the absence 

 of anything new, I may as well notice the following sentence : — ■ 

 " We do not know," says Liebig, " in what form the constituent 

 parts of organic matter are produced." This knowledge is properly 

 the ultimate object of physiology, but those who apply themselves 

 to this science are not contented with " mere images, having no 

 other end but to render those processes comprehensible and they 

 ask, with some reason, wherefore Dr. Liebig, after having produced 

 such a testimonium paupertatis, should pour forth his calumnies upon 



