THE CAUSE OF PULSATION 485 



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 Scyphomedusae, 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: 



Na,CA + CaCL =2NaCI + CaC 2 4 , 

 >fa 2 CA + < 'aS< > 4 = Xa,S0 4 + Ca (',(),. 



