Od the Electric Organ in Malapterurus electricus. 435 



modified ; the rate of transit of the photographic plate upon which the 

 image of the mercurial meniscus was projected, was made much quicker, 

 whilst the whole organ of the fish was effectually cooled to a low tem- 

 perature, 5° C. 



As we had only one fish, we made several attempts to catch a record 

 of the natural discharge of the organ upon the travelling plate. It 

 was found, however, to be practically impossible to do this, since the 

 reflex responses obtained from the uninjured fish were not merely un- 

 certain as to their time of commencement but also very variable as to 

 their intensity. 



We determined, therefore, to kill the fish and utilise the nerve 

 organ preparation for the purpose of obtaining the necessary data. 



A further consideration induced us to take this course. Determina- 

 tions made upon an entire fish must be of little value for the calculation 

 of the E.M.F. of the change produced in each excited disc, owing to 

 the complicated physical conditions of an experiment made under these 

 circumstances. On the other hand it appeared to be easy to cut an 

 organ strip and arrange it so that the distance between the contacts, 

 which connected it with the electrometer, should be perfectly definite ; 

 moreover, with such a strip the number of discs comprised in the actual 

 distance between the contacts could be enumerated after the experi- 

 ment by examining appropriate sections made through the whole of 

 this portion of the organ. 



The fish was therefore anaesthetised by immersion in ice-cold water 

 and then killed. A strip of the organ was now detached and the nerve 

 carefully dissected out ; this nerve organ preparation was placed upon 

 a glass plate in a special moist chamber kept at a uniform temperature 

 of 5° C. The nerve was excited by a single break induced current of 

 such an intensity as our previous experience had shown to be neces- 

 sary in order to evoke a maximal organ response (Kronecker coil with 

 core, one Daniell in primary, secondary at 10,000). The break induc- 

 tion shock was produced by the movement of the recording pendulum, 

 and was so timed as to occur when the photographic plate carried by 

 the pendulum reached the slit upon which the image of the meniscus 

 w T as projected. The electrometer contacts were so placed as to lie 15 

 mm. apart upon the thickest portion of the organ. Thirteen photo- 

 graphs were taken, of which two (Nos. 3012, 3013) gave excellent 

 records suitable for accurate analysis. In the first of these (3012), a 

 facsimile reproduction of which is shown in fig. 1, the three-lamp 

 shunt was placed between the electrometer terminals. In the second 

 record (3013) the two-lamp shunt was employed. 



The response in both these experiments was very marked, and, 

 owing probably to the low temperature, was more delayed in its onset 

 and slower in its development than we had anticipated. 



After comparatively few successful experiments the excitability of 



