88 DYNAMICS OF LIVING MATTER 



sea water do contractions begin. It differs in this regard very markedly 

 from Gonionemus, whose center begins to beat at once in a pure NaCl 

 solution. After a certain time, however, generally a number of hours, 

 rhythmical contractions will begin in the isolated center of Polyorchis 

 in a pure NaCl solution, and may last with long interruptions for two 

 or three days. When they have ceased in a pure NaCl solution, a few 

 single contractions can at any time be produced by touching the subum- 

 brella with a drop of a solution of a potassium salt; but the addition 

 of a potassium salt to the NaCl solution, although it promptly calls 

 forth a single contraction or a short series of contractions, does not 

 maintain the rhythm. 



A sure means of producing rhythmical contractions of the isolated 

 center of Polyorchis at once in a pure NaCl solution is the addition of 

 a certain amount of a salt which precipitates Ca, or diminishes the 

 concentration of the Ca-ions, e.g. Na-citrate, -tartrate, -oxalate, etc. 

 I generally used the citrate as it seems to be the least harmful. If 

 lo c.c. of a w sodium citrate solution be added to a loo c.c. | n NaCl 

 solution, rhythmical contractions of the isolated center begin usually 

 at once, and may last an hour or more. A second means of calling forth 

 rhythmical contractions in a pure solution of NaCl at once is the addi- 

 tion of a trace of an acid, e.g. HCl. COj acts in the same way, and I 

 have wondered whether this acid which is formed regularly in the body 

 does not thus play an important r61e in rhythmical contractions in 

 general. The addition of acids may even cause the center to beat in 



n 

 sea water. About 1.5 to 2 c.c — HCl to 100 c.c. of sea water is required 



for this purpose. Alkalis have the opposite effect. The action of the 

 acid may be the same as that of the oxalate and citrate; namely, to 

 set free Ca, which is in organic combinations in the cells, or at the surface 

 of the cells, and make thus a substitution of Na or K for Ca, or vice 

 versa, in these organic compounds, possible. It may be mentioned 

 here that the oxalates, citrates, and similar salts, and the acids, are 

 believed to play such a rdle in the process of the coagulation of milk.* 

 One of the promptest means of producing rhythmical contractions in 

 the isolated center of Polyorchis is putting it into a pure solution of 

 CaClj, BaClj, or SrCl^. Instead of dissolving the CaCl^ in distilled 



water, it may be dissolved in a | m or — sugar solution in order to have 



a solution which is more nearly isosmotic with sea water. If an isolated 

 center is put into a solution of 10 c.c. J m CaClj + 50 c.c. | m cane sugar 



* A. S. Loevenhart, Hopfe-SeyUr's Zeitschr. fur physiologische Chemie, Vol. 41, p. 177, 

 1904. 



