ON THE STUDY OF ZOOLOGY 363 



a muscle contract at one time and not at another ? Why 

 does one whole group of muscles contract when the lobster 

 wishes to extend his tail, and another group when he 

 desires to bend it? What is it originates, directs, and 

 controls the motive power ? 



Experiment, the great instrument for the ascertainment 

 of truth in physical science, answers this question for us. 

 In the head of the lobster there lies a small mass of that 

 peculiar tissue which is known as nervous substance. 

 Cords of similar matter connect this brain of the lobster, 

 directly or indirectly, with the muscles. Now, if these 

 communicating cords are cut, the brain remaining entire, 

 the power of exerting what we call voluntary motion in the 

 parts below the section is destroyed; and on the other 

 hand, if, the cords remaining entire, the brain mass be 

 destroyed, the same voluntary mobility 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 peculiar energy which resides in the nerves 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 ascertain upon what arrangement, or other condition 

 of the molecules of matter, the manifestation of the nervous 

 and muscular energies depends, (and doubtless 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 successfully 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 determining 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 



