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,’ Howell,’ 
and Greene*® 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. 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: 
100 c.c. % NaCl 
100 c.c. % NaCl-+ 4 c.c. +55 Ca(Nos3)2 
100 c.c. # NaCl-+-1 c.c. +55 Ca(Nos)2 
100 c.c. % NaCl-+ 2c.c. +3 Ca(Nos3)2 
100 c.c.  NaCl+4c.c. 1 Ca(No3)2 
100 c.c.  NaCl-+ 8 c.c. 75s Ca(Nos3)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 8 to 5, 
OOP ON 
1 AUBERT, Pfltigers Archiv, Vol. XXIV (1881), p. 361. 
2 HOWELL, American Journal of Physiology, Vol. II (1898), p. 47. 
3 GREENE, ibid., p. 82. 4 Part II, p. 559. 
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