OPENING ADDKESS. 7 



mine function; it limits it, it prescribes the mode in 

 which the activity shall especially manifest itself and that 

 only. It is only in this sense true " that every appreciable 

 difference in structure corresponds to a difference of 

 function."* 



The inference is, however, often correct and I will now 

 refer to those demonstrative examples of the correctness 

 of the inference and the dangers which beset it, which 

 are afforded by the examination of a class of special 

 organs — the socalled electrical organs present in certain 

 fishes. 



More than a century ago I it was discovered that the 

 peculiar numbing power possessed by certain sea fish, 

 (Torpedo or Electric Ray) was due to the power they 

 possessed of being able to discharge electric currents of 

 great intensity, these being generated in organs in the 

 body of the fish. These organs, when investigated by 

 John Hunter anatomically, were found to consist of piles 

 of thin plates arranged in columns and supplied by an 

 enormous number of nerves and nerve branches. When 

 a muscle contracts a great many things happen besides 

 the change in form and among these is the generation of 

 electrical effects ; but one special aspect of its activity — 

 that of contraction — transcends all others. In the elec- 

 trical organ, an electromotive disturbance occurs in the 

 neighbourhood of each nerve ending and this now far 

 transcends any other aspect of its activity. 



Another fish, this time a fresh-water one, the Gymnotus 

 or Electric Eel, found in the Orinoco, was known to 

 possess the power. When it was examined anatomically, 

 also by Hunter, it was found to have four enormous 



* Sanderson. British Association, Address, Section D, 1889. 

 tSee Phil. Trans., 1773 : Discovery by Dr. Walsh, j>. 461, and Anatomical 

 investigations by John Hunter. 



