352 COMPARATIVE ELECTRO-PHYSIOLOGY 



former being the more characteristic of the fresh condition, 

 and the latter of a specimen which has been previously sub- 

 jected to continuous stimulation. Before giving any account, 

 however, of these electrical responses, it will be interesting 

 to demonstrate here the occurrence of secretion in young or 

 fresh specimens, when subjected to excitation. The fact 

 that young rootlets secrete, on excitation by contact, has 

 already been seen in the well-known experiment on the 

 corrosion of marble, mentioned above. But I shall now 

 describe a new experiment, in which this fact is even more 

 convincingly demonstrated. I took a specimen of Colocasia, 

 growing in marshy soil. The plant was lifted bodily, with 

 earth adhering, and placed in water, so as to expose the 

 roots gradually, without causing injury. It was then kept 

 overnight, with the roots in normal saline solution, which 

 was slowly absorbed by the tissues. Next morning, again, 

 it was carefully washed till there was no trace of salt ad- 

 hering. One of the very young roots was now immersed 

 in very dilute solution of silver nitrate. If the previous 

 washing had oeen effective, there ought now to be no white 

 precipitate, or only the merest trace, formed in the silver 

 solution. The two electrodes of a RuhmkorfT's coil were 

 next connected, one with the silver solution, and the other 

 with the stem of the plant. On now passing tetanising 

 shocks, the immersed root became excited, and secreted its 

 contained salt solution, this being seen in the silver nitrate as 

 streams of white precipitate. 



Turning next to the electrical mode of investigation, we 

 have found that in the digestive organs, the galvanometric 

 negativity, which is the characteristic response of a specimen 

 in the fresh condition, becomes reversed to positivity under 

 continuous stimulation. In the case of Nepenthe, very young 

 pitchers exhibited this normal response of negativity, which 

 was converted, under continuous stimulation, into diphasic, 

 tending towards positivity. Older specimens, again, pre- 

 viously stimulated by the presence of excitatory food-material, 



