EFFECTS OF SODIUM AND CALCIUM. 39 



ever, that the addition of CaCOa, which improves the regularity of 

 pulsation of Medusae in NaCl + K2SO4, has only the effect of neutral- 

 izing acids. Distilled water and the purest obtainable salts were used 

 in making solutions and there is no reason to suppose that there were 

 any more free acids in the solutions than in the natural sea-water itself. 



Physiologists have generally assumed (see Howell, Text-Book of 

 Physiology, p 502) that the chief r61e of sodium chloride in pulsa- 

 tion is to maintain the osmotic pressure of the solution. I find, how- 

 ever, that Cassiopea pulsates more than 24 minutes in a solution of 

 Na2S04 containing the same amount and proportion of Na as is found 

 in sea-water ; whereas it will not pulsate more than 14 minutes in a 

 solution of Na3S04 isotonic with sea-water. This would lead one to 

 believe that the sodium of the sea-water exerts a specific action, and 

 that the salts have a specific chemical effect independent of their 

 osmotic action. Indeed, the various salts of sodium behave very 

 differently ; for example, Cassiopea pulsates less than i minute in 

 Na2C03, II to 12 minutes in NaClOa, and more than half an hour in 

 NaCl, or NaNOs isotonic with sea-water. 



When pulsations have ceased in 96 c.c. HjO -1-2.7 grams NaCl 4- 

 0.085 gram K2SO4 they may be revived temporarily by NajCOs, more 

 NaCl, KCl, K2CO3, or weak acids. These cause only a few irregular 

 contractions, however, and are quite different in their effects from 

 the long, steady revival of pulsation upon the addition of calcium. 

 Potassium is, however, capable of reviving temporary pulsation in 

 any solution which lacks magnesium, but if magnesium be present it 

 can not usually revive pulsation. It is interesting to observe that 

 after Medusae have ceased to pulsate in the NaCl + K2SO4 and have 

 been revived by potassium, they will not again pulsate upon the addi- 

 tion of calcium to the solution. On the other hand, if pulsations have 

 ceased and have been revived by adding more sodium, they can be 

 revived a second time by adding calcium. Potassium in excess at 

 first stimulates the disk powerfully, but soon it poisons the tissues and 

 inhibits the sensibility, while calcium is not a stimulant, but is neces- 

 sary for pulsation in connection with sodium and potassium. The 

 chief r61e of calcium is, however, to counteract the inhibiting effect 

 of the magnesium. 



This is shown by the fact that if we were to place Cassiopea in nor- 

 mal sea-water, and then add suflScient sodium oxalate to precipitate 

 the calcium, pulsation ceases in less than five minutes, but is quickly 

 restored if we place the Medusa in NaCl + KCl -I- sodium oxalate, or 

 in NaCl -1- KCl. Pulsation is not restored, however, if we place the 

 Medusa in NaCl -I- magnesium. These experiments prove that the 



