48 PULSATION OF JELIvYFlSHES. 



When we proportionately reduce the sodium chloride and mag- 

 nesium, but at the same time maintain the amounts of calcium and 

 potassium of the sea-water, the rate of pulsation and general energy 

 of the Medusae steadily decline. This was done by diluting sea -water 

 with distilled water containing the amounts of calcium and potassium 

 found in sea-water, as is described on page i8. If we simply dilute 

 the sea-water with distilled water the rate of pulsation does not decline 

 so rapidly, and the injurious effects are not so pronounced. 



These experiments show that a relative excess of Ca and K retards 

 pulsation, even when the actual amounts of Ca and K are such as are 

 found in sea- water. 



Cassiopea will pulsate longer in LiCl 4- KjSO^ -I- CaSO^ than in a 

 solution wherein the NaCl is replaced by NagCOa. In these solutions 

 the IviCl and NagCOs were isotonic with the NaCl of sea-water, while 

 the amounts of K and Ca were the same as are found in sea-water. 

 The Medusae ceased pulsating in about 6 minutes in the LiCl solution , 

 but it seems somewhat remarkable, in illustrating the effects of salts 

 as a whole, that LiCl should replace the NaCl with less injury than 

 Na^COs. 



"We have seen that NaCl in excess or in pure solutions has very little 

 toxic effect upon Cassiopea. This appears remarkable, for its marked 

 toxic effects have been made known by Loeb, Lingle, Cushing, and 

 others upon a number of animals, and I find that pure solutions of 

 NaCl have a very rapidly injurious effect upon the movement of the 

 branchial arms of Lepas. We must remember, however, that Cassiopea 

 normally lives in semi-stagnant salt-water lagoons where considerable 

 range in density must take place through evaporation and rainfall. 

 It is also one of the most hardy of marine animals and will survive 

 without serious effects several minutes' immersion in sea-water con- 

 taining such poisons as o.i per cent KCN. 



It will be recalled that Macallum (1903) found that while the amount 

 of NaCl in brackish estuaries might change greatly with the condition 

 of the tide, the amount of NaCl in the bodies of the Aurelia and Cyanea 

 remained practically constant. It is therefore possible that Cassiopea 

 may resist osmosis of NaCl to some extent and thus avoid its possibly 

 toxic influences. 



We conclude that NaCl is a stimulant and is counteracted in this 

 respect by the magnesium of sea-water so as to produce a balanced 

 solution. It can not maintain pulsation except in connection with 

 calcium and potassium, in combination with which it forms a powerful 

 stimulant which produces a rapid but only temporary pulsation, mag- 

 nesium being necessary to reduce and sustain its action. 



