108 fag Stniictts, (Essays, sntr gcbictos. [vi. 



has been found to be accompanied 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 as certain upon what arrangement, or other 

 condition of the molecules of matter, the manifestation of 

 the nervous and muscular energies depends, (and doubt- 

 less science will 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 suc- 

 'cessfully performed for all the operations which are 

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

 would be perfect, and the facts of morphology and 

 distribution would be deducible from the laws which 

 physiologists had established, combined with those deter- 

 mining the condition of the surrounding universe. 



There is not a fragment of the organism of this humble 

 animal, whose study would not lead us into regions of 

 thought as large as those which I have briefly opened 

 up to you ; but what I have been saying, I trust, has not 

 only enabled you to form a conception of the scope and 

 purport of zoology, but has given you an imperfect 

 example of the manner in which, in my opinion, that 

 science, or indeed any physical science, may be best 

 taught. The great matter is, to make teaching real and 

 practical, by fixing the attention of the student on par- 

 ticular facts ; but at the same time it should be rendered 

 broad and comprehensive, by constant reference to the 

 generalizations of which all particular facts are illustra- 

 tions. The lobster has served as a type of the whole 

 animal kingdom, and its anatomy and physiology have 



