EFFECT OF IONS UPON TISSUE 561 



the margin, and inasmuch as the whole Gonionemus is just 

 as immune against the Ca and K ions of the sea-water as 

 the margin, it follows that the normal contractions of the 

 Gonionemus originate in the part which contains the ganglia. 

 It is probable, moreover, that the margin and the center 

 must contain the three metal ions (Na, Ca, and K} in differ- 

 ent proportions. That this is only a difference in degree, 

 however, is proved by the fact that an increase in the amount 

 of K and Ca ions above that of the sea-water will finally 

 stop the rhythmical contractions of the margin. On the other 

 hand, it is probable that a very small amount of K and Ca 

 ions, smaller than that in the sea-water, allows the center to 

 beat rhythmically. 



This difference between the margin and the center is not 

 the same in all Medusae. If we cut off the margin in an 

 Acalepha (for instance, Aurelia aurita), the center begins to 

 beat in sea- water a short time after the operation. It is 

 possible that a comparative study of the heart-beat would 

 reveal similar facts. 



We have thus far shown that the center of a Gonionemus 

 is able to beat for about an hour in a pure NaCl solution, 

 while the whole Gonionemus or the margin is able to beat in 

 a NaCl solution containing in addition a small amount of K 

 and Ca ions. How does a whole Gonionemus behave in a 

 pure NaCl solution? As stated above, the contractions of 

 Gonionemus occur in sea- water in groups followed by long 

 pauses. If a Gonionemus be put into a ^n NaCl solution, 

 the swimming-bell contracts without interruption and the 

 rate of contraction increases considerably. It may within 

 two minutes reach a rate of 200 contractions per minute, but 

 soon ceases to beat. If the In NaCl solution be diluted 



o 



with distilled water, the increase in the rate of contractions 

 occurs more slowly and the contractions continue longer. If 

 we use a solution of 98 c.c. n NaCl + 2 c.c, y n CaCl 9 , it 



