40 PULSATION OF JELLYFISHES. 



pulsation is inhibited by the magnesium of the sea-water, not merely by 

 the loss of calcium ; for pulsation may be restored in solutions which 

 lack calcium. They also show that when calcium is present the 

 magnesium does not inhibit pulsation. 



EFFECTS OF MAGNESIUM UPON PULSATION. 



The magnesium salts in sea- water retard pulsation in Cassiopea, and 

 reduce its rate, amplitude, and energy. Cassiopea pulsates at about 

 twice its normal rate in a solution resembling sea-water but lacking 

 magnesium, but if we add the magnesium to this solution the Medusa 

 immediately pulsates at normal rates. Also, an excess of magnesium 

 added to sea- water causes the rate and energy of pulsation to decline, 

 although Medusae will tolerate 1.6 grams MgCl 2 in 100 c.c. sea-water, 

 and will pulsate slowly for half an hour without the least apparent 

 injury, their normal rate being regained in a few minutes after they 

 are returned to pure sea-water. Magnesium acts only as a restrainer, 

 never stimulating the disk of Cassiopea. When the disk, deprived of 

 marginal sense-organs, is placed in a solution of MgCl 2 or MgSO 4 

 isotonic with sea- water it does not pulsate. Indeed, the rate of pulsa- 

 tion of normal Medusae in natural sea-water becomes successively 

 slower as we add more and more magnesium. 



The r61e of magnesium is, however, an essential one in pulsation, 

 for it counteracts the strongly stimulating action of the combination 

 of NaCl, K, and Ca which occurs in Ringer's solutions, or in sea-water. 

 For example, if we place Cassiopea in a solution of NaCl + KCl + CaCl 2 

 in amounts and proportions found in sea-water * the Medusa is highly 

 stimulated and pulsates at fully twice its normal rate. If now we pre- 

 cipitate the magnesium in its tissues in any manner, f the stimulating 

 effect of the sodium, potassium, and calcium is unchecked, and after a 

 short period of violent pulsation the Medusa passes into a strong sus- 

 tained tetanus and remains motionless, with its bell highly contracted. 



I find also that sustained pulsation is impossible in the heart of 

 Salpa or the branchial arms of Lepas unless magnesium be present, 

 and that in these cases also NaCl+KCl +CaCl 2 is a powerful stimu- 

 lant, producing rapid but not permanently sustained pulsation, but 

 normal sustained pulsation is attained on the addition of magnesium. 

 It appears, therefore, that a Ringer's solution is not an inorganic food 

 for the pulsating organ, as has been commonly assumed by physiol- 



*100 NaCl + 2.2 KC1 + 3 CaCl 2 all of >n concentration, as in Van 't Hoff's solu- 

 tion. 



f The magnesium maybe precipitated by a small amount of Ba(OH) 2 , KOH, NaOH, 

 or sodium phosphate -}- ammonia -f- ammonium chloride, etc. 



