754 STUDIES IN GENERAL PHYSIOLOGY 



parallel to the edge we can divide the animal into a marginal 

 part, which contains the central nervous system, and a cen- 

 tral part, without a central nervous system. 



When this operation is performed, the margin will go on 

 beating in sea-water, while the center will not beat. Ro- 

 manes, who was (as I believe) the first to make this experi- 

 ment, drew the conclusion that the central nervous system 

 was the originator of the automatic contractions of this 

 animal. From previous experiments of Aubert, 1 Howell, 2 

 and Greene 3 on the heart, and my own experiments on the 

 muscles, I concluded that the center of a jelly-fish (Gonio- 

 nemus) did not beat in sea-water on account of the presence 

 of certain ions in sea- water, especially calcium, and I showed 

 that the center of a Medusa will beat rhythmically in pure 

 NaCl or NaBr solution. 4 The center of a Medusa whose 

 margin is cut off seems then to behave, to a certain extent, 

 like the striped muscle. It was of some importance to 

 find out how far this analogy goes. The following six solu- 

 tions were prepared: 



1. 100 c.c. NaCl 



2. 100 c.c. ? NaCl + c.c. tV Ca(No 3 ) 2 



3. 100 c.c. f NaCl + 1 c.c. -& Ca(No 3 ) 2 



4. 100 c.c. f NaCl + 2 c.c. -ft Ca(No 3 ) 2 



5. 100 c.c. ~ NaCl + 4 c.c. ft Ca(No 3 ) 2 



6. 100 c.c. NaCl + 8 c.c. ft Ca(No 3 ) 2 



In solution 1 the center of a Medusa begins at once to con- 

 tract very rapidly. The velocity of contractions steadily in- 

 creases and very soon it becomes impossible to count the 

 contractions. Occasionally the same happens in solution 2. 

 But in the solutions 3 to 6 the center at first remains per- 

 fectly quiet. After a latent period of about ten minutes, 

 often, but not always, contractions begin in solutions 3 to 5, 



1 AUBEET, Pfliigers Archiv, Vol. XXIV (1881), p. 361. 



2 HOWELL, American Journal of Physiology, Vol. II (1898), p. 47. 



3 GREENE, ibid., p. 82. * Part II, p. 559. 



