THE METAMORPHOSIS. 447 



descriptions of muscles, however, may be affected in the same manner 

 by one and the same excitement, for electricity effects both a contraction 

 of the heart and the same phenomena in the muscles of the limbs. 



The first thing we perceive in the activity of any determinate muscle 

 is a contraction of itself. By means of this contraction its compass 

 enlarges, its texture feels more compact and firmer, and the entire 

 muscle is in a state of excitement. How this excitement is produced 

 we know not, but thus much is ascertained, that the nerves exercise 

 great influence upon the motions of the muscles. But the nature of 

 this influence we must leave undetermined whether, as some physiolo- 

 gists suppose, generation produces the necessary power for acting upon 

 the muscles, or whether, with others, it be to be considered as merely 

 the conductor of the excitement from its point of production to the 

 muscle. We are most fully convinced of the importance of the influence 

 which the nerves exercise upon the motion of the muscles when galvanic 

 electricity is applied to a nerve and a muscle standing in connexion 

 with it, or upon its application to the former alone. Alexander von 

 Humboldt, whose great genius first announced itself in a surprising 

 manner in the illustration of this difficult and then insufficiently- 

 laboured field of physiology, has supplied us with some interesting 

 observations, even in reference to insects *. He saw animated con- 

 tractions in the limbs when the nerves passing to them were touched 

 by the poles of a voltaic pile, re-actions which continued for a space of 

 twenty minutes, and which admitted of being prolonged three times 

 that space upon the nerves being artificially prepared with alkalis and 

 oxidised muriatic acid. He also observed in the thigh of a B/atta 

 orientali.i, touched with gold and zinc, from two to three successive 

 shocks ; indeed " the thigh raised itself up, and held itself some 

 seconds trembling in the air." He further remarks : " Upon galvanising 

 the spinal marrow of a Blattn orientalis with silver and well-burnt 

 carbon, I observed its posterior portion move to and fro and press with 

 its feet." Even in the body of a Fespa crabro, the head of which 

 had been cut off fourteen hours before, the same admirable observer saw 

 the limbs tremble upon the application of the metallic stimulus. 



This trembling of the limbs after the effect of galvanic electricity 

 speaks also in favour of an oscillation of the muscular fibres in insects as 

 well as in the superior animals. This oscillation was formerly denied 



* Ueber die gereizte Muskel-und Nervenfaseir. Berlin, 1797. 8vo. vol. 1, p. 273. 



