130 Papers from the Marine Biological Laboratory at Tortugas. 



Urea and uric acid are relatively passive in so far as pulsation is con- 

 cerned, but the presence of crystals in the sense-organs containing- calcium 

 oxalate acquires a meaning when we recall the fact that the sense-organs 

 can not maintain pulsation unless they be constantly supplied with soluble 

 calcium from the sea-water. 



We see at once that there must be some oxalate which is constantly 

 forming- in the sense-organs, and which is precipitating the soluble calcium 

 chloride and sulphate derived from the sea-water to form the insoluble calcic 

 oxalate crystals of the sense-club. 



The question before us is, what oxalate is being formed in the sense- 

 organs? We know that in certain tissues in the bodies of animals oxalic 

 acid and other oxalates are formed apparently through the incomplete 

 oxidation of carbo-hydrates. I find that I part by weight of oxalic acid in 

 1000 parts by weight of sea-water quickly paralyzes the sense-organs so 

 completely that they do not recover the power of initiating pulsation even 

 after they are returned to sea-water. So weak a solution of oxalic acid is, 

 however, not a stimulant to the subumbrella tissue, nor is it appreciably 

 poisonous to the medusa as a whole. 



From i to 5 parts by weight of the oxalates of potassium and magnesium 

 in 1000 parts of sea-water also inhibit pulsation after a short initial stimula- 

 tion, and it can not be that these are the cause of pulsation in the sense-organs. 



If, however, we immerse the sense-organs in a solution of from i to 5 

 parts by weight of sodium oxalate in 1000 parts by weight of sea- water, they 

 are powerfully stimulated, and give forth pulsations at a rapid rate ; but 

 on the other hand this weak solution has no stimulating effect if applied to 

 the subumbrella alone. 



Now sodium oxalate precipitates the calcium which enters the sense- 

 organ from the sea-water, forming calcium oxalate, and sets free sodium 

 chloride, and sodium sulphate; both of which are powerful nervous and 

 muscular stimulants. The formula for this reaction is as follows : 



Na 2 C 2 O 4 + CaCl 2 = 2NaCl + CaC 2 O 4 , 

 Na,QO 4 + CaSO 4 = = Na 2 SO 4 + CaC 2 O 4 . 



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

 excess of sodium over and above that found in the sea-water, and this acts 

 as a stimulant which is prevented from becoming too concentrated by the 

 fact that being in solution it is constantly passing out into the surrounding 

 sea-water. 



We can prove experimentally that this suffices to explain the phenomenon 

 of pulsation, for if we simply add from i to 5 parts of sodium chloride to 

 1000 parts of sea-water, we find that this slight excess of salt acts as a 

 powerful stimulant if applied to the sense-organs, but produces no pulsation 

 if placed upon parts of the jelly-fish other than the sense-organs. 



