562 STUDIES IN GENERAL PHYSIOLOGY 



contracts much more slowly, but the contractions last longer. 

 In a solution of 98 c.c. f n NaCl + 2 c.c. f n KC1 it does 

 not beat at all, with the exception of a few contractions at 

 the beginning. In a solution of 96 c.c. f n NaCl -f 2 c.c. 

 -|n KCl-(-2 c.c. y n CaCl 2 it beats very slowly, but much 

 longer than in any other of the solutions mentioned. In 

 pure -|n KC1 or ^ n Ca01 2 solutions no contractions 

 occur. 



The explanation of all these facts seems to me to be as 

 follows : If a Gonionemus be put into a pure NaCl solution, 

 Na ions begin to enter the tissues. As soon as they contain 

 a certain number of Na ions, any further increase of the Na 

 ions raises the rate of contractions. On the other hand, 

 the substitution of Ca and K ions for Na ions has the 

 opposite effect (as long as not too many Na proteids are 

 formed). If too many Na ions have entered into combina- 

 tion with the proteids, the irritability ceases. We shall see 

 later that in this case the substitution of Ca or K ions for 

 Na ions restores the irritability. 



Thus the Na ions play an important rdle in the rhythmical 

 contractions. It is just as necessary that a certain number 

 of Na proteids exist in the tissues of the Gonionemus as 

 that a certain number of Ca and K proteids be present. 

 The proportion of these three proteids is, however, apparently 

 different in the margin and in the center. In both kinds of 

 tissue the relative number of Na proteids is greater than 

 that of the other proteids. 



The view differs from the one generally held in connec- 

 tion with the heart-beat, that the NaCl in the blood serves 

 mainly the purpose of preventing the tissues from losing or 

 taking up water, 1 while the Ca salts are considered as the 

 cause of the systole and the KC1 is said to favor the diastole 

 of the heart. The fact that a Medusa not only contracts 



1 HOWELL, American Journal of Physiology, Vol. II (1898), p. 47. 



