RHYTHMIC PULSATION 349 



plotted, only in the presence of MgS04 is the sodium effect com- 

 pletely abohshed. This was quite uniformly observed. MgS04, 

 in combination with NaCl, KCl, and CaCl2, led to pulsations of 

 a normal character, whereas MgCL did not do so, not completely 

 at least, even in mixtures where the quantity of Mg normally 

 derived from MgS04 + MgCU was ''made up" by a calculated 

 amount of MgCl2. The deficiency of solutions lacking magne- 

 sium lay in the fact that, as Loeb ('06) observed with the medusa 

 Polyorchis, in these mixtures the sphincters tended to contract 

 permanently, in more or less tetanic fashion. MgCl2, and espe- 

 cially MgS04, and more particularly both together, acting with 

 the other salts of sea water, led to normal relaxations after each 

 systole, and thus tended to preserve a normal rate and duration 

 of pulsation. Solutions containing NaCl and MgCl2 or MgS04, 

 or both, did not maintain rhythmic movements as long as con- 

 trols in NaCl; CaCl2 and KCl were necessary for the complete 

 balance of the solution, as regards pulsation. 



This applies to artificial salt mixtures. They were practi- 

 cally neutral in reaction. An attempt was made to approach the 

 problem from the other side, by precipitating the SO4" out of sea 

 water by BaCl2. Solutions prepared in this way preserved pulsa- 

 tion for not quite so long (about 4 hours) as did the neutral 

 van't Hoff mixture. The effect noted in the absence, of MgS04 

 in artificial salt combinations may therefore have been due, in 

 part, to the particular Ch. of those mixtures (cf. Loeb, '10). 



It is unnecessary to go into the analysis of many of the results 

 obtained with salt mixtures, since they are so similar to those 

 which have been found for other pulsating structures (Robertson, 

 '10). Certain findings with reference to the significance of Ca- 

 in pulsation may however be mentioned. From table 12 it 

 will be seen that the antagonism between Na •• and Ca was a 

 very imperfect one as regards the duration of pulsation, though 

 good as determined by the preservation of irritability. Between 

 Na- and K" there was no antagonism. Na- + K' + Ca- formed 

 a nearly completely balanced solution, aside from the K" and Ca- 

 tetanising effects, which interfered with normal diastolic relaxa- 

 tion. The preservation of irritability was not very much less 



