XXVIII 



ON THE DIFFERENT EFFECTS OF IONS UPON MYO- 

 GENIC AND NEUROGENIC RHYTHMICAL CON- 

 TRACTIONS AND UPON EMBRYONIC AND MUSCULAR 

 TISSUE > 



I. ON THE DIFFERENT EFFECT OF IONS UPON THE MARGIN 

 AND THE CENTER OF A HYDROMEDUSA (GONIONEMUS) 



IN a preceding paper 2 I gave a number of facts which 

 force us to assume that not the salts themselves, but their 

 ions, are in combination with the proteids, and that the 

 physical qualities of the various ion- proteids are different. 

 This being true, a pure solution of an electrolyte ought to be 

 poisonous, and I have been .able to prove that a pure NaCl 

 solution of the strength in which marine animals live kills 

 them in a comparatively short time. The addition of a small 

 amount of certain other metal ions (K and Ca) renders the 

 solution harmless. This supports the assumption that irri- 

 tability depends upon the various ions, especially the metal 

 ions (Na, Ca, K, and Mg] existing in definite proportions 

 in the tissues. But as each tissue has its own specific irri- 

 tability, it would follow that various tissues must possess the 

 various ions in different proportions. This paper contains 

 the result of a series of investigations on this subject. 



Gronionenras propels itself by rhythmical contractions of 

 its swimming-bell. The swimming-bell, however, does not 

 contract continuously, like the heart, but in groups of 

 rhythmical contractions, followed by longer pauses. The 

 swimming-bell of the Medusa may be divided into two 

 regions, a marginal region containing the double nerve ring 



1 American Journal of Physiology, Vol. Ill (1900), p. 383. 



2 Part II, p. 544. 



559 



