178 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



Eimer and Romanes found that if the marginal sense organs be 

 removed the jellyfish is paralyzed and responds only by single con- 

 tractions to external stimuli. Later, in 1906, Mayer found that if 

 the sense organs be removed and we cut a ring-shaped or circuit- 

 shaped strip of tissue from the concave part of the bell, we may 

 then start a contraction wave proceeding in one direction through the 

 circuit through which it travels continuously, being, indeed, en- 

 trapped by the circuit of tissue from which it can not escape. This 

 movement is almost machinelike in its regularity, its rate being about 

 440 cm. a second, and in 1917 McClenden showed that this note 

 remained practically unchanged even though the nerves were arti- 

 ficially stretched. 



It is interesting to see that the pulsation stimulus in jellyfishes is 

 conducted by the nerves, whereas in the vertebrate heart it is con- 

 ducted by the muscles. There is, however, as Parker showed, a 

 fundamental likeness between nervous and muscular activity, for in 

 most essential features, such as the compensating pause following 

 an extra pulsation and the refractory stage during systole, latent 

 period, reaction to temperature, etc., the jellyfishes behave as does 

 the vertebrate heart. In Europe Romanes, Bethe, and von Uexkull,. 

 and in America Loeb, Harvey, Cary, McClenden, and Mayer have 

 been most active in these studies. 



Recently Mayer finds that nerve conduction in Cassiopea is a 

 chemical reaction in which the cations of sodium, calcium, and po- 

 tassium take the active part, while magnesium is nonessential. Thus 

 if we dilute the sea water with 0.4 molecular magnesium chloride 

 the rate of pulsation declines only very slightly more than if we 

 diluted it with distilled water, thus demonstrating the inert nature 

 of magnesium in respect to the rate of nerve conduction. It is also 

 interesting to see that this decline in rate is proportional to the 

 decline in the concentration of the cations of sodium, calcium, and 

 potassium which surround the nerves and not to the electrical con- 

 ductivity of the sea water as a whole. Thus if we dilute with dis- 

 tilled water we decrease the electrical conductivity in nearly the 

 same ratio as the dilution, while if we dilute with 0.4 molecular 

 magnesium chloride the electrical conductivity remains nearly con- 

 stant while we simply reduce the concentration of the sodium, cal- 

 cium, and potassium cations. It is therefore these cations which 

 are alone essential to the maintenance of the rate of nerve conduction. 

 The previous work of Mayer, 1906, Meltzer and Auer, 1908, and 

 especially Osterhout, 1916, make it appear that sodium and calcium 

 together combine with some proteid element forming a sodium- 

 calcium-ion proteid, and this compound takes an essential part in 

 nerve conduction. Mayer in 1916 showed that the rate of nerve con- 

 duction in the medusa Cassiopea has a temperature coefficient 2.5 times 



