STIMULI AND THEIR ACTIONS 



455 



5* Galvanotaxis 



It is characteristic of the galvanic current that it always calls 

 out phenomena of polar excitation. As a result of this, stimulation 

 by the constant current is especially well fitted to exercise directive 

 effects. Since, further, the current can be graduated in intensity 

 very delicately, arid its direction can be readily controlled, it affords 

 a very perfect means of producing experimentally directive reactions 

 in their most exact form, and with the certainty of physical pheno- 

 mena. The galvanotactic phenomena of motile 

 organisms remind one of the effects of the 

 magnet upon iron particles. 



The galvanotactic phenomena of animals 

 were first discovered by Hermann ('85), in the 

 larvae of frogs and the embryos of fishes. He 

 observed that when a galvanic current was 

 conducted through a vessel containing these 

 animals, upon the making of the current all 

 placed themselves with their long axis parallel 

 with the curved lines of flow of the current, 

 so that their heads were directed toward the 

 anode and their tails toward the kathode. In 

 this position they remained. Analogous effects 

 have been observed more recently and upon 

 various other higher animals by Nagel ('92, '93, 

 '95), Blasius and Schweizer ('93), and latest 

 by Loeb('96, 2, 3, 4; '97,1,2). 



Galvanotactic phenomena have also been 

 found in plants, especially the root-tips of 

 many plants ; when the constant current is 

 sent through them for a considerable time, the 

 tips bend toward the kathode. 



But most striking, and theoretically most 

 interesting, are the phenomena, in free-living 

 unicellular organisms, such as Rhizopoda, leuco- 

 cytes, Infusoria, etc. 1 



In order to investigate the galvanotaxis of 

 these organisms, we can best employ the above- , 



described slide with non-polarisable clay-electrodes, or non-polaris- 

 able electrodes that are arranged like camel's-hair brush-electrodes 

 but, instead of the brush, have tips made of fired clay which can be- 

 dipped into the liquid through which the current is to be sent 

 (Fig. 229). 



If a few drops of water containing many Paramcecia be placed 

 on the slide between the parallel pieces of clay that serve as 



1 Cf. Verworn ('89, 2, 3 ; j'92, 2 ;i'96, 4) and Ludloff ('95). 



PIG. 229. Non-polaris- 

 able electrode, which, 

 instead of the camel's- 

 hair brash has a tip 

 made of fired clay. 



