Papers from the Marine Biological Laboratory at Tortugas. 



51 



the hydrogen ion concentration of the solution from about 6.5 to 9. Thus 

 the inhibiting effect of the Mg was offset by the addition of an alkali. 



It appears from my experiments of 1906 that calcium can not produce 

 tetanus unless sodium be present, for in the absence of sodium even pure 

 solutions of 0.4 molecular CaCl2 do not produce tetanus in Cassiopea, and 

 if the medusae be stupefied in magnesium they can not be temporarily re- 

 vived by calcium unless sodium be present. These observations are in 

 accord with those of Meltzer and Auer on mammals, wherein they found 

 that the inhibiting tendency of magnesium is offset by a calcium-sodium 

 combination, not by calcium alone. 



As in all experiments of this series, normal medusae are much more 

 sensitive to the effects of magnesium than are rings. In other words, as 

 is always the case, the motor centers are more readily affected than are the 

 peripheral nerves. 



EFFECTS OF THE POTASSIUM ION. 



We may maintain the normal osmotic pressure and increase the con- 

 centration of the potassium ion by adding to the sea-water a 0.64 molecular 

 solution of KCl. Even so small an amount as 3.75 c.c. of this solution 

 added to 100 c.c. of sea-water stops all movement in normal medusae after 

 an initial excitement which soon subsides. The peripheral nerves, on the 

 other hand, are not so readily affected as the motor centers, for a ring still 

 pulsated at about two-thirds its normal rate when placed in 100 c.c. sea- 

 water -f- 7.5 c.c. of 0.64 molecular KCl. 



A 



3 D 

 Relative Concentration of K 

 Fig. 12. 



Table 15 and figure 12 illustrate the results of experiments with potassium. 

 The rates stated in figure 12 are the actual rates assumed by animals after 

 being at least 45 minutes in the solutions mentioned, the volume of solution 



