148 ELECTRICITY AND PROTOPLASM [Ch.TI 



closely allied beetles like Dytiscus and Hydrophilus should 

 by the same observers be found to react in different ways. 



In addition to the species named, some have been studied 

 which have given no results. Thus Nagel ('95, p. 639) ob- 

 tained no response from the larva of Libellula depressa, even 

 with a wide range of current-intensities. 



Passing now to the Vertebrata, we enter a region in which, 

 as a result of more numerous studies, the data are more volu- 

 minous, but at the same time less in accord. Since many mat- 

 ters are here still in dispute, we may best consider historically, 

 i.e. in chronological sequence, what has hitherto been done in 

 this field. 



The first person to describe the phenomenon of electrotaxis 

 in Vertebrates — as, indeed, in any organism • — was Hermann 

 ('85, '86). He used frog larvae 14 days old, held in a shallow 

 rectangular porcelain trough, along the two small sides of which 

 thick zinc wires were placed, connected with a chain of 20 small 

 zinc-carbon elements. No mention of the strength of the cur- 

 rent except such as can be gained from these facts was made. 

 This omission of quantitative details is to be regretted, since 

 had the strength of current to which the organisms were sub- 

 jected been given, much subsequent confusion might have been 

 avoided. With this current, then, of unknown intensity, flow- 

 ing through the water containing the larvae, all of the latter 

 were seen to place themselves in the axis of the current with 

 their heads directed toward the anode. This orientation was 

 the consequence of the fact that a current passing cephalad 

 through the larva acted as a violent stimulus ; but while 

 passing caudad it brought stupefaction or even (temporary) 

 paralysis. 



The results obtained by Hermann were now confirmed and 

 extended by Blasius and Schweizee ('93). They employed 

 a wooden trough with sheet zinc electrodes of nearly the cross- 

 section of the smaller ends of the trough, and experimented 

 upon fishes, Salamandra, and the frog. The weakest current 

 employed was 0.35 S to 0.47 8, which merely affected the char- 

 acter of the swimming of the fish subjected to it, without 

 determining its direction. The next stronger current men- 

 tioned was 1.58 8. With this current a marked orientation of 



