44 



ELECTROLYTES IN BIOLOGICAL SYSTEMS 



what reduced compared to the controls (fig. 4). Light also prevents an increase 

 in sodium when the inhibitor concentration is raised to 0.005 m/1. 



Influence of iodoacetate in the light and the dark: Valonia. The presence of 

 the inhibitor at a concentration of o.ooi m/1. causes no significant change in the 

 potassium and sodium content of cells placed in the light and dark for a period 

 of at least 300 hours. When the concentration of iodoacetate is raised to o.oi 



Fig. 4. Influence of iodoacetate on the sodium content of Ulva lacluca in the light and in 

 the dark. Sodium is expressed in terms of dry weight. 



m/1., however, a marked loss of potassium and gain of sodium ion occurs for a 

 period of 250 hours, changes which do not occur in the controls in light and 

 dark without the inhibitor. In the presence of light the inhibitor is completely 

 inefifective (fig. 5). Similar experiments in which the concentration of inhibitor 

 was raised to 0.02 and 0.03 m/1. respectively gave essentially similar results 

 with the potassium-loss and sodium-gain curves displaced slightly to the left. 

 In all three experiments light prevented the iodoacetate effect; in fact, in the 

 illuminated samples with the inhibitor the potassium was somewhat higher 

 than in the controls. The similarity between Ulva and Valonia in this experi- 

 ment is striking. 



