SENSATION 



of their roots (very sensitive organs, compared by 

 Darwin to the brain of the animal), they bend towards 

 the cathode. 



Many of the protists are very sensitive to electric 

 currents, as Max Verworn especially proved by a series 

 of beautiful experiments. Most of the ciliated infusoria 

 and many of the rhizopods (amceba) are cathodically 

 sensitive or negatively galvanotactic. When we send a 

 constant electric current through a drop of water in 

 which thousands of paramcecium are moving about, all 

 the infusoria swim at once, with the anterior pole of the 

 body foremost, towards the cathode or negative pole; 

 they accumulate about it in great crowds. If the direc- 

 tion of the current is now changed, the whole swarm at 

 once make in the opposite direction for the new cathode. 

 Most of the flagellate infusoria do just the reverse ; they 

 are anodically sensitive or positively galvanotactic. In a 

 drop of water, in which swarms of polytoma are moving 

 about, all the cells swim at once towards the anode or 

 positive pole, when an electric current is sent through. 

 The opposite galvanotropic behavior of these two 

 groups of infusoria in a drop of water, in ^hich they are 

 mixed together, is very interesting; as soon as a constant 

 stream enters it, the ciliata fly to the cathode and the 

 flagellata to the anode. When the current is reversed 

 the two swarms rush at each other like hostile armies, 

 cross in the middle of the drop, and gather at the op- 

 posite poles. These and other phenomena of galvanic 

 sensation show clearly that the living plasm is subject to 

 the same physical laws as the water that is decomposed 

 into hydrogen and oxygen by an electric current. Both 

 elements feel the opposite electricities. 



SCALE OF SENSATION AND IRRITABILITY 



ist Stage: Sensation op Atoms. Affinity of the elements in 

 every chemical combination. 



313 



