214 THE STUDY OF ZOOLOGY Til 



tion is destroyed ; and, on the other hand, if, the 

 cords remaining entire, the brain mass be destroyed, 

 the same voluntary mobihty is equally lost. 

 Whence the inevitable conclusion is, that the 

 power of originating these motions resides in 

 the brain and is propagated along the nervous 

 cords. 



In the higher animals the phenomena which 

 attend this transmission have been investigated, 

 and the exertion of the pecuhar energy which 

 resides in the nerves has been found to be accom- 

 panied by a disturbance of the electrical state of 

 their molecules. 



If we could exactly estimate the signification 

 of this disturbance ; if we could obtain the value 

 of a given exertion of nerve force by determining 

 the quantity of electricity, or of heat, of which it 

 is the equivalent; if we could ascertain upon 

 what arrangement, or other condition of the 

 molecules of matter, the manifestation of the 

 nervous and muscular energies depends (and 

 doubtless science wiU some day or other ascertain 

 these points), physiologists would have attained 

 their ultimate goal in this direction ; they would 

 have determined the relation of the motive force 

 of animals to the other forms of force found in 

 nature ; and if the same process had been success- 

 fully performed for all the operations which are 

 carried on in, and by, the animal frame, physiology 

 would be perfect, and the facts of morphology 



