Papers from the Marine Biological Laboratory at Tortugas. 41 



90 per cent as concentrated as in natural sea-water. Below this the rate 

 declines, becoming normal in 80 per cent sea-water and from this point down- 

 ward it declines in a straight-line ratio, at a somewhat more rapid rate than 

 the corresponding decline in concentration of the dissociated electrolytes. 



The curve as a whole reminds one of that of an enzyme reaction having 

 its maximum in 90 per cent sea-water and rising in a straight line from 50 

 to 80 per cent. This does not prove, however, that it has anything to do 

 with enzyme action. 



It will be recalled that Loeb (1891) discovered that growth and regen- 

 eration in hydroids proceeds at a somewhat more rapid rate in sea -water 

 diluted with 15 to 20 per cent distilled water than in normal sea-water. 

 The experiments of Goldfarb (1907) upon the regeneration and growth 

 rate in hydroids and his more recent observations upon Cassiopea^ confirm 

 this fact. Loeb ascribed the increase in rate of regeneration to the effects 

 of potassium and magnesium, but Goldfarb's observations cast doubt upon 

 this simple explanation. It is clear that the initial increase in the rate of 

 nerve-conduction in Cassiopea, which accompanies the decline in con- 

 centration of the electrolytes below the normal, is not due to lowered os- 

 motic pressure, for it occurs when the sea-water is diluted with 0.9 molecular 

 dextrose, thus maintaining the osmotic pressure found in normal sea-water. 



A possible but purely hypothetical explanation may be that if the rate 

 of nerve-conduction is due to an excess of ionic sodium in the tissues over 

 and above its concentration in the surrounding sea-water, a slight lowering 

 of the concentration of the sodium in the sea-water causes a corresponding 

 increase in its ratio of concentration within the tissues and may thus cause 

 an augmentation in the stimulus. There is some evidence to support this 

 view, for when the sea-water is diluted with 0.487 molecular sodium chloride, 

 the rate does not increase as rapidly as it does when the sea-water is diluted 

 with distilled water or with dextrose. The slight initial increase in rate 

 when the sea-water is diluted with 0.487 molecular NaCl may be due to the 

 reduction of the potassium ion which in such concentration is a stimulant, 

 as is sodium. 



THE RELATION BETWEEN THE RATE OF NERVE-CONDUCTION AND THE 

 CONCENTRATION OF THE SODIUM ION. 



In order to test the effect of the sodium cation upon the rate of nerve- 

 transmission, we may add increments of a solution of 0.6 molecular NaCl 

 to the sea-water, thus maintaining a constant and normal osmotic pressure, 

 but increasing the concentration of Na while the concentrations of Mg, 

 Ca, and K are decreased. 



The physical effects of such a procedure are illustrated in table 7, showing 

 that if we add 0.6 molecular NaCl up to 100 sea-water + 800 NaCl we have 

 changed the concentration of the sodium ion from i to 1.205; while at the 

 same time, in comparison with the Mg, Ca, and K, the Na ion has become 

 relatively 10.85 times as concentrated as it was in natural sea-water. 



1 See Dr. Goldfarb's paper upon the rate of regeneration of Cassiopea in concentrated, normal, and 

 diluted sea-water; page 88 of this volume. 



