THE CAUSE OF PULSATION 487 



Tims the sodium oxalate which foims in the sense-organs is simply 

 changed into ordinary table salt, which acts as a stimulus to produce 

 pulsation. 



We can prove experimentally that this suffices to explain the phe- 

 nomenon of pulsation, for if we simply add from 1 to 5 parts of com- 

 mon salt to 1,000 parts of sea-water, we find that this slight excess 

 of salt acts as a powerful stimulant to the sense-organs, but produces 

 no pulsation if placed upon other parts of the jellyfish. 



It thus appears that each sense-organ normally maintains a certain 

 excess of common salt which acts as a stimulus, and which is prevented 

 from becoming too concentrated by the fact that being soluble it is 

 constantly dissolving out into the surrounding sea-water. 



It may trouble us for a moment to see why a recurrent pulsation 

 should arise from a constantly present stimulus, but long ago Romanes 

 discovered that a weak constantly present stimulus, such as a faradaic 

 current of electricity, will cause rhythmical pulsation, the jellyfish 

 responding to it periodically and regularly. 



We see then that the natural stimulant which produces the pulsa- 

 tion of the jellyfish is only that most familiar substance common salt ! 



The hearts of higher animals behave in a manner so similar to that 

 of the pulsating jellyfish that we neecl not be surprised if it be demon- 

 strated that here also a slight excess of sodium chloride gives rise to 

 each and every pulsation. 



