396 OF NERVOUS IRRITABILITY 



manifested, in the foregoing experiments, by its effect upon the con- 

 tractile muscles. But we shall hereafter see that this is, in reality, 

 only one of its results, and that it shows itself, during life, by a 

 variety of other influences. Thus it produces, in one case, sensa- 

 tion; in another, muscular contraction; in another, increased or 

 modified glandular activity; in another, alterations in the pheno- 

 mena of the circulation. The force, however, which is exerted by 

 a nerve in a state of activity, and which brings about these changes, 

 is not directly appreciable in any way by the senses, and can be 

 judged of only by its secondary effects. We understand enough 

 of its mode of operation, to know that it is not identical with the 

 forces of chemical affinity, of mechanical action, or of electricity. 



And yet, by acting upon the organs to which the nerves are 

 distributed, it will finally produce phenomena of all these different 

 kinds. By the intervention of the muscles, it results in mechanical 

 action ; and by its influence upon the glands and bloodvessels, it 

 causes chemical alterations in the animal fluids of the most import- 

 ant character. 



It will even produce well-marked electrical phenomena, which 

 in some cases are so decided, as to have long attracted the attention 

 of physiologists. 



It has been fully demonstrated that certain fish (gymnotus and 

 torpedo) have the power of generating electricity, and of producing 

 electric discharges, which are often sufficiently powerful to kill 

 small animals that may come within their reach. That the force 

 generated by these animals is in reality electricity, is beyond a 

 doubt. It is conducted by the same bodies which serve as con- 

 ductors for electricity, and is stopped by those which are non-con- 

 ductors of the same. All the ordinary phenomena produced bj 

 the electric current, viz : the heating and melting of a fine con- 

 ducting wire, the induction of secondary currents and of magnetism, 

 the decomposition of saline solutions, and even the electric sparkj 

 have all been produced by the force generated by these animals. 

 There is, accordingly, no room for doubt as to its nature. 



The electrical phenomena, in these cases, are produced by certain 

 organs which are called into activity by the nervous influence. 



The electrical organs of the gymnotus and torpedo occupy a con- 

 siderable portion of the body, and are largely supplied with nerves 

 which regulate their function. If these nerves be divided, tied, or 

 injured in any way, the electrical organ is weakened or paralyzed, 

 just as the muscles would suffer if the nerves distributed to them 



