i8o NATURE AND MAN. 



the standpoint afforded by the " correlation " doctrine, we are 

 led to question whether the project of the Laputan sage to ex- 

 tract sunbeams from cucumbers was so very chimerical after all , 

 while we cannot but feel an increased admiration of the intuitive 

 sagacity of that remarkable man George Stephenson, who Avas 

 often laughed at for propounding in a somewhat crude form the 

 very idea which we have just been endeavouring to present under 

 a more philosophical aspect. 



There are other modes, however, in which the living animal 

 restores to the universe the forces which the plant took from it. 

 Its most distinguishing attribute is motion ; and this motion being 

 another expression of force, the question arises, What is the source 

 of that force ? There, again, we fall back on the plant, both for 

 the force, and for the material of the structure which exerts it. 

 All the higher forms of animal motion are the result of Muscular 

 contraction ; and physiologists are now generally agreed in the 

 truth of the statement first formally enunciated by Liebig, that 

 every act of muscular contraction involves the death and oxida- 

 tion of an amount of muscular substance proportional to the force 

 exerted. Hence we are justified in regarding the motion produced 

 by this contraction as an expression of the vital force which is 

 superseded by chemical action, and as holding the same relation 

 to that chemical action which the voltaic current bears to the 

 oxidation of the zinc in the battery. Going further back, we 

 find that the peculiar nitrogenous material of which muscle is 

 composed, though organized by the animal under the agency 

 already explained, is really generated by the plant ; and that its 

 production in large amount may be regarded as the highest effort 

 of plant-life, taking place as it does only under the most favourable 

 concurrence of conditions, among which a copious supply of light 

 and heat are especially required. And thus we may say that the 

 nitrogenous constituents of plants embody a high degree of force, 

 which is destined ultimately to manifest itself in the sensible 

 motions of animals. And it is a curious confirmation of this 

 view, that if these substances pass into decomposition without 

 being organized into muscle, they set free a large amount of 

 chemical force; all those "ferments" which have so remarkable 

 a power of exciting chemical changes in other organic compounds, 

 being members of this group. 



