10 Papers from the Marine Biological Laboratory at Tortugas. 



arms thrust straight outward without being recurved or crooked at the 

 ends. Cassiopea soon flattens out, and the Eunicidae and Nereidae come 

 to rest in relaxed, smoothly-flowing folds. 



On the other hand, in solutions containing calcium but lacking 

 magnesium we find that Lepas comes to rest with its branchial arms 

 contracted and strongh' recurved at their tips. Cassiopea tears its 

 bell through muscular tetanus, and the annelid worms set themselves 

 into rigid, distorted, sharply-twisted, "kinked" shapes, with spasmodic, 

 local twitchings of the longitudinal muscles due to clonic tetanus, and 

 often rents are torn through the cuticula, thus permitting the body- 

 fluids to escape. 



If, however, we have both magnesium and calcium in the solution 

 they tend, in the presence of sodium, to offset one the other, the mag- 

 nesium preventing tetanus and the calcium preventing complete relax- 

 ation. We see, however, that in the Na -\- Mg -|- Ca row the branchial 

 arms of Lepas still tend to recurve at their ends as in calcium solutions, 

 showing that the magnesium has not completely offset the calcium in 

 this respect, although the pedicel is as fully relaxed as in magnesium 

 solutions. It will be recalled that Meltzer and Auer, in a series of well- 

 known and able papers have called prominent attention to the anesthetic 

 (or asphyxiating ^ ) influence of- magnesium when introduced into the 

 blood-system of vertebrates, and in 1908, in the American Journal of 

 Physiology (vol. 21, p. 400), they announce that the effects of a lethal 

 dose of magnesium upon a rabbit can be counteracted by a subsequent 

 injection of calcium salt into its blood-system. 



The drawings also show the strong stimulating effect of sodium, for 

 in 0.625 molecular NaCl, Lepas comes to rest after abnormally active 

 movements of its branchial arms, with its pedicel strongly contracted 

 and usually with its shells shut and arms withdraw^n; although in the 

 specimen I have figured the arms are slightly projecting with their tips 

 strongly recurved, this being the only solution save those containing 

 calcium, which commonly causes a "crooking" of the tips of the arms. 

 The medusa and the annelids move with abnormal rapidity in NaCl 

 but come to rest without tetanus, although not in so completely relaxed 

 a state as when in Na -{- Mg. 



Thus the effect of ionic sodium, magnesium, potassium, and calcium 

 is in each case of the same nature in all of these invertebrates. Sodium 

 stimulates, magnesium depresses, potassium, after a momentary stimu- 

 lation, depresses," and calcium depresses and produces tetanus in each of 

 these animals; as, indeed, they do also in their effect upon the ganglia 

 that control the heart of Limulus, according to Carlson, 1906 (Amer. Jour- 



* See Guthrie and Ryan, 1910, American Journ. Physiol., vol. 26, p. 329. 



^ In experimenting upon Annehds and Cassiopea I find that the initial stim- 

 ulus caused by the addition of a slight concentration of potassium to the sea-water 

 can be counteracted if we add together with the potassium about 5.5 times the 

 amotmt of magnesium in a solution isotonic with the potassium. As this is about 

 the ratio of potassium to magnesium in normal sea-water, it is probable that the 

 primarily stimulating effect of the potassium is offset by the magnesium of the sea- 

 water, and thus the potassium of the sea-water may be considered as a simple 

 depressant. 



