Converse Relation between Ciliary and N euro-Muscular Movements. 13 



crystal of NaCl, while the part is twitching in tetanus, it responds by a 

 vigorous contraction which travels immediately throughout the length 

 of the worm. This leads one to conclude that the calcium tetanus is 

 myogenic, not neurogenic. 



Calcium-tetanus, as is well known, can be counteracted by magne- 

 sium, but in order to stupefy marine animals without any trace of distor- 

 tion, one should use a pure 0.4 molecular MgClz or a molecular MgSO^ 

 solution, which are practically isotonic with the NaCl of sea-water and 

 which produce a complete relaxation of the muscles without any con- 

 siderable initial stimulation. In this respect they are more efficient and 

 much quicker in action than a mere excess of magnesium in sea-water. 



In solutions containing ionic sodium any calcium which may be 

 present tends to counteract the depressant effects of magnesium; but 

 if sodium be absent the calcium has no power to offset the inhibiting 

 tendency of magnesium. It seems therefore that the calcium ion com- 

 bines with the sodium and forms a compound which is capable of over- 

 coming the inhibiting effects of the magnesium. 



In order to demonstrate the inability of calcium to offset the inhibit- 

 ing effect of magnesium in a solution lacking sodium, I cut ten Cassiopea 

 medusse into quadrants. One quadrant of each medusa was placed in 

 MgCl2, another in MgClj + CaCL,, another in MgCl2 -f KCl, and the 

 fourth quadrant in MgCl2 -H CaCl2 + KCl; the proportionate parts of 

 the Mg, Ca, and K being those found in sea-water. The result is shown 

 in the following table, wherein the medusae are numbered from I to X 

 and the number of pulsations given by each quadrant of each medusa 

 before coming to final rest is shown in the vertical columns. It will be 

 seen that adding Ca to solutions of Mg or of Mg -f K does not overcome 

 their depressant powers. The medusae come to rest after a very few 

 pulsations in Mg, or Mg -f- Ca, but the addition of potassium causes a 

 characteristic initial stimulus which sustains movement for a longer 

 time than it can endure in pure Mg or Mg -\- Ca. Weak concentrations 

 of the potassium ion are always a primary stimulant for the neuro- 

 muscular system and an initial depressant for ciHa, and the potassium 

 does not combine with any of the other metalHc ions to produce this 

 effect, but is itself competent to produce it. 



Table showing the number of pulsations given by ten Cassiopea xamachana medus(S. 



[Each is cut into quadrants and each of the quadrants placed in one or the other of the 4 solutions 

 shown below: — Medusas numbered I to X.] 



It may be of some interest to observe that the palolo worm, Eunice 

 fucata, if in the dark, writhes vigorously when stimulated by the Hght 

 of a match or an incandescent electric lamp. This reaction is not due 



