Papers from the Marine Biological Laboratory at Tortugas. 



49 



and in the interval the solution was changed several times. In this manner 

 an attempt was made to permit the animal to become thoroughly permeated 

 by a solution before its effect was tested. 



Table 14. 



Tables 13 and 14 show the average conditions; table 13 referring to the 

 rate of nerve-conduction in the rings without motor centers, and table 14 

 to the pulsation of medusae with motor centers intact. It is evident that 

 any excess of magnesium causes a rapid decline in rate in the perfect medusae. 



In rings of subumbrella tissue 0.4 molecular MgCl2 causes a decline in 

 rate of nerve-conduction which is but little more pronounced than that 

 observed when the sea-water is diluted with diitilled water or with 0.9 

 molecular dextrose. 



This leads one to conclude that the magnesium ion is inert rather than 

 an active repressor of nerve-conduction. If this be the case all concen- 

 trations of MgCU from 0.4 molecular downward should behave alike and 

 should exert the same influence as distilled water or 0.9 molecular dextrose. 



Sea wa-t er 



2?<»C 



/oo SeSL Wetter 4- « o ^^1^01^ .f-jn. 

 4- 2.0 



100 



I o o 



i 00 



+-30 ' 



■H -4-0 



2.9 s 



I 00 



+ 50 



Fig. 10. 



2.7.7 



Figure 9 appears to show that this expectation is largely realized, the effects 

 of 0.057 molecular and of 0.4 molecular MgCl2 being closely similar to those 

 of distilled water, and while 0.4 molecular MgCl2 may exert a slight specific 

 depressant effect, it is evident that the concentration of Mg found in sea- 

 water (0.057 molecular) is not more depressant than is distilled water. 



