560 STUDIES IN GENERAL PHYSIOLOGY 



and its ganglia, and the central region which has no ganglia, 

 but is said to possess scattered ganglion cells. The case is 

 similar to that of the heart, which has ganglia in the auricles 

 and sinus vinosus, whose ventricle, however, is free from 

 ganglia, but contains scattered ganglion cells. 



Romanes first stated that if we cut a Hydromedusa in 

 two, the marginal part with the ganglia will continue to beat 

 rhythmically very much like the whole Medusa, while the 

 center ceases to beat. These results have been confirmed by 

 several authors, but I have found that the statement of 

 Romanes is only correct for sea-water. If the center of a 

 Hydro-medusa be put into a pure ^n NaCl or ^n NaBr solu- 

 tion, it begins to beat rhythmically for an hour immediately 

 after the operation. Hence the center as well as the margin 

 is capable of spontaneous contractions. But why does the 

 center not beat rhythmically in sea-water? If it be put in- 

 to a solution of 98 c.c. -|w NaCl + 2 c.c. y n CaCl 2 , it no 

 longer beats rhythmically. The same is true for a solution 

 of 98 c.c. |n NaCl + 2 c.c. |n KC1, or a solution of 96 

 NaCl -f 2 CaCl 2 + 2 KCL Hence the Ca and K ions of the 

 sea- water prevent the center from beating rhythmically. 



This harmonizes with my previous experiments on the 

 muscles of the skeleton. 1 The latter are able to beat rhyth- 

 mically in a pure NaCl or a NaBr solution or any solution 

 with Na ions. But a small addition of Ca ions or K ions, or 

 both, prevents rhythmical contractions. We owe it to the 

 presence of these ions in our blood that our muscles do not 

 contract rhythmically like the heart. 



Thus we see that there is a typical difference between the 

 effects of ions on rhythmical contractions originating in the 

 muscles directly and those originating in parts which con- 

 tain ganglia or which originate in the latter themselves. 

 Inasmuch as the whole Gonionemus beats in the rhythm of 



1 Part II, p. 518. 



