ELECTROLYTES IN LIVING MATTER 8 1 



edge of a Hydromedusa be cut off from the center, the former continues 

 to beat while the latter stops beating. This fact was utilized as an 

 argument to prove that the contractions in a Medusa originate normally 

 from the nerves in the margin. This may be so, but it seemed to me 

 that the center of a Medusa (deprived of its nerve ring) might also be 

 able to beat if it were not prevented from so doing by the constitution 

 of the sea water. I found, indeed, that the isolated center of Gonio- 

 nemus, a Hydromedusa, common at Woods Hole, is able to beat rhyth- 

 mically in a pure solution of NaCl.* The center beats in such a solu- 

 tion very rapidly, and the more rapidly the higher, within certain hmits, 

 the concentration of the NaCl solution. The addition of a small quan- 

 tity of CaClj or MgClj retards or inhibits the contractions caused in 

 the NaCl solution. If a salt which precipitates Ca or diminishes the 

 concentration of its ions is added in excess to sea water (e.g. sodium 

 oxalate, fluoride, citrate), the center can be caused to beat in sea water 

 also. 



It is thus obvious that the case of the center of the Medusa seems 

 very analogous to that of the muscle. Just as the latter is prevented 

 from twitching in the blood on account of the presence of CaClj and 

 MgCL,, so the isolated center of Gonionemus is prevented from beat- 

 ing in sea water on account of the presence of CaClj and MgCl^. 



After these data had been obtained I asked Dr. Lingle to deter- 

 mine whether similar laws hold for the heartbeat. It was known that 

 if the sinus venosus of a frog's heart be severed from the heart, the 

 former goes on beating as before ; while the rest of the heart, especially 

 the isolated ventricle, stops beating in blood. This observation is 

 comparable to the one made by Romanes on jellyfish; and we may 

 carry the analogy a step farther, by comparing the center of the Medusa 

 to the ventricle ; the edge to the sinus venosus of a frog's heart. Lingle 

 worked on the heart of a tortoise, f He found that the ventricle is only 

 able to beat after it has been put for about half an hour into a pure 

 solution of NaCl. When the ventricle remains permanently in the 

 sodium chloride solution, the heartbeats will stop after a certain time, 

 as Lingle believes, on account of the diffusion of too much NaCl into 

 the heart muscle. If the strip of the ventricle is put into a moist chamber 

 after the beats are once started in a NaCl solution, they may continue 

 for a number of days, until the process of putrefaction puts an end to 

 the contraction. No other substance can take the place of Na. Li, 

 which acted so well in the case of the isolated frog's muscle, can be 

 only partially substituted for NaCl. One of the most remarkable 



* Loeb, Am. Jour. Physiology, Vol. 3, p. 383, 1900. 



t D. J. Lingle, Atn./our. Physiology, Vol. 4, p. 265, 1900 ; Vol. 8, p. 75, 1902. 



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