VI.] 



CURRENT-DENSITY 



113 



A 



generally happened that this necessary condition obtained in 



my earliest experiments, for the tubes of both electrodes were 



of equal bore, and any excess of fluid around them was removed 



by filter paper. But failing 



this precaution, we should be 



liable to have unequal effects, 



due to unequal current densi- 



ties at the two poles. If the 



inequality is very marked, we 



shall obtain greater response 



from the pole of smaller area 



(i.e.. where current density is 



J 



greater), whether that pole be 



anode or kathode. The fact 



deserves to be illustrated by an 



experiment ad hoc. Here then 



is a living surface it happens to be a vegetable surface to 



which two electrodes of different area are applied ; the exci- 



tation is applied first in one then in the other direction, and 



as you see, both the responses are in the same direction, 



ingoing at the pointed electrode, whether that electrode has 



been anodic or kathodic. 



Will some one be good enough to repeat this experiment 

 on a piece of frog's skin ? I should expect him to find both 

 responses to be outgoing at the pointed electrode, instead of 

 ingoing as in the vegetable surface.* 



* This has since been verified by Dr Alcock. 



FlG> 



REFERENCES 



HERMANN u. LUCHSINGER. " Ueber die Secretionsstrome der Haut bei 



der Katze," Pfliiger's Archiv, xvii., p. 310, 1878. 

 WALLER. " On Skin-currents. Observations on Cats," Proc. Roy. Soc., 



vol. 69, p. 171, 1901. 

 BIEDERMANN. "Ueber Zellstrome" (Frog's Tongue), Pfliiger's Archiv, 



liv., p. 209, 1893. 

 BOHLEN (BlEDERMANN). "Ueber die elektromotorischen Wirkungen rde 



Magenschleimhaut," Pfliiger's Archiv, Ivii., p. 97, 1894. 

 BIEDERMANN. "Elektrophysiologie," Jena, 1895 (translated by Miss F. A. 



Welby. Macmillan & Co., 1896-98). 



H 



