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 1 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 1 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: 
NasCO;, = CaCl, ==2NaCl-— CaGoy 
Na, C/Op-- CaSO, = NaSO,-- CaCO; 
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 1 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. 
