nervous in nature, and travels through the nervous tissue quite inde- pendent of the presence or absence of the muscles. When therefore the magnesium paralyzes the muscles the nervous stimulus still travels around the ring even though the muscles can not now respond to it by contraction.
We now are in a position to state that each pulsation is due to a nervous stimulus which originates somehow in the sense-organs. The question is, how does it originate ?
In all of the large jellyfishes called Scyphomedusæ, the marginal sense-organs are little clubs, the axial cores of which always contain a terminal mass of crystals. These crystals consist of calcium oxalate with a slight addition of uric acid and urea. The uric elements are relatively inert and need not be further considered. The presence of calcium oxalate, however, acquires some meaning when we find that the sense-organs can not continue to give rise to pulsations unless they be constantly supplied with soluble calcium, and all movement ceases in a few moments if the jellyfish be placed in sea-water deprived of calcium. 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 of 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 carbohydrates. Now we find that even so small a quantity as one part by weight of oxalic acid in one thousand parts of sea-water paralyzes the sense-organs and permanently prevents their giving rise to pulsation, although so weak a solution is not sen- sibly poisonous to the general tissues of the medusa. Also the oxalates of potassium and magnesium finally inhibit pulsation, and it can not be that any of these is the cause of pulsation in the sense-organs.
The key to the mystery seems to be found, however, when we im- merse the sense-organs in a solution of from 1 to 5 parts of sodium oxalate in 1,000 parts of sea-water; for this immediately stimulates them into great activity, whereas it has no effect if applied to any part of the medusa other than the sense-organs.
Now sodium oxalate precipitates the calcium which enters the sense- organ from the sea-water to form calcium oxalate, and sets free common salt and sodium sulphate ; both of which are powerful nervous and muscular stimulants. The chemical formula for .this reaction is as follows:
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