548 



Miscellaneous. 



whole families of Euphorbiacese, Asclepiadese, Milky Cacti, &c., con- 

 sist of large thin-sided cells filled with watery juice and a little 

 chlorophyll. Among them are distributed a few thick-sided vessels 

 filled with a milky juice, which contains but little water. These 

 vessels are not mechanically united with the first class of cells, and 

 perhaps even their organic connexion may not be important. In 

 despite of this milky juice, the watery matter of the cells would soon 

 evaporate if it were not protected by the close texture of the epider- 

 mis. A person who applies to vegetable physiologists a language 

 like that used by Dr. Liebig, should, we think, endeavour to under- 

 stand at least the elementary principles of vegetable physiology. It 

 is needless to produce more instances of this kind, which may be 

 found on nearly every page ; our assertions will be abundantly sup- 

 ported by what still remains to be introduced. 



It must be considered as an unavoidable consequence of the haste 

 with which Liebig has worked, of his striking want of scientific 

 knowledge, and of the little consideration he has given to his subject, 

 that his reasoning may be refuted point by point, even in matters 

 where his views are just. In my opinion there is nothing which 

 proves more evidently the uselessness of an author, than the circum- 

 stance, that his reasoning is open to well-founded objections while 

 his evidence is admitted. Such a man cannot fail to create a preju- 

 dice against science itself, because many will imagine that they have 

 put an end to a subject, however solid its foundation, when the 

 defence of it by a weak advocate has been easily thrust aside. I feel 

 it my duty to state this expressly, as many persons would otherwise 

 blame me for having attacked Liebig on account of views which I 

 myself have defended at other times. My object in writing this paper 

 is not to treat of certain laws and principles of physiology, but to 

 show, what Dr. Liebig does not understand — the problems which 

 that science has to solve ; and that at least, in this publication, he 

 has not in any essential way contributed to the solution of these pro- 

 blems. In order to proceed regularly in the performance of this task, 

 I shall subject the principal sections of his work, as far as they regard 

 vegetable physiology, to a more exact and minute examination. 



The first section (from 6 to 43) treats of the assimilation of car- 

 bonic acid. I have already mentioned that he begins with stating 



