90 DYNAMICS OF LIVING MATTER 



sugar, than in a mixture of CaCl 2 and NaCl solutions ;* but the antagonism 

 is not complete, and I have actually obtained contractions in a mixture 

 of NaCl + CaCL, in a center of Polyorchis. It can be shown that the 

 Mg-salts contained in the sea, water inhibit the muscular contractions. 

 If we start rhythmical contractions in a mixture of 50 c.c. f m NaCl + 

 10 c.c. m Na-citrate, and then put the center into a pure NaCl solution, 

 or a solution of 50 c.c. NaCl + i or 2 c.c. CaCl 2 , the center continues to 

 contract. If, however, the center be put into a solution of 50 c.c. f m 

 NaCl + 5 c.c. | m MgCL, the contractions are inhibited. I believe that 

 it is generally more due to the MgCL, than to the CaCl 2 that an isolated 

 center of a Medusa does not beat in normal sea water. 



The facts thus far described give no clear answer to the question 

 whether the substitution of NaCl or KC1 for CaCl 2 or the reverse process 

 causes the contraction. Possibly the following observation may throw 

 light on this problem : If an isolated center is put into 50 c.c. f m cane 

 sugar + 10 c.c. f m CaCl 2 contractions will begin, which continue when 

 the center is put into 50 c.c. m cane sugar -f 10 c.c. m sodium citrate; 

 but if the center is put from the latter into the former solution, it stops 

 beating at least for some time. Various modifications of this experiment 

 give similar results : they seem to speak in favor of the idea that the 

 substitution of Na or K for Ca causes a contraction ; but the evidence is 

 by no means unequivocal. 



The question may be asked how it happens that in a pure solution 

 of NaCl the beats do not start at once, but only after a number of hours. 

 Is it necessary that NaCl enter the cells of the Medusa, and that this 

 process requires time? Were this the reason, we should expect that 

 within certain limits an increase in the concentration of the NaCl solu- 

 tion should accelerate the beginning of the contractions. I have not 

 been able to find that this is true. The contractions began about 

 equally late in a |- m and a -|, |-, or | m NaCl solution. I am more 

 inclined to believe that the Ca must enter into an appropriate com- 

 bination in the muscles, and, for that purpose, must be freed from 

 another combination which is responsible for the delay in the beginning 

 of the spontaneous contractions of the center of Polyorchis in a pure 

 NaCl solution. The beats of the center begin in a pure NaCl solution 

 when the muscle cells of the center have had time to free an abundant 

 amount of calcium from an organic combination contained in them. 

 This might be done by a hydrolytic enzyme directly or indirectly, in 

 the latter case through the influence of an acid, e.g. CO 2 , in the muscle 

 cells. This supposition has its analogue in the action of rennet in the 



* Tt is possible that this antagonism is due to the fact that the NaCl and CaCl 2 retard 

 each other's diffusion into the cells. 



