142 



ISAAC STARR, JR. 



B. Observed 18 Hours after Return to Sea Water. 



Isotonic NaCl at at- 

 mospheric oxygen 

 tension. 



1/2 larvae show 

 bend ings 



1/50 larvae show 2/50 larvae show 

 bendings bendings 



Isotonic NaCl at 

 approx. 756 mm. 

 oxygen tension. . . 



1/50 larvffi show 

 bendings 



No motion 



No motion 



Sea water at approx. 

 756 mm 



Normal 



Normal 



Some heliotropic, 

 some not helio- 

 tropic. all other- 

 wise normal. 



The increase in toxicity caused by the excessive oxygen tension 

 is very marked. 



The writer wishes to express his thanks to Professor R. S. 

 Lillie under whose direction the problem was undertaken. 



CONCLUSIONS. 



1. The removal of most of the oxygen from the solution 

 markedly diminishes the toxicity of sodium chloride isotonic to 

 sea water to Arcnlcola larva;. 



2. Slight increases in oxygen tension also markedly diminish 

 the toxicity of isotonic sodium chloride. 



3. Saturation with oxygen markedly increases the toxicity of 

 this solution. 



4. At a tension of approximately 2/5 mm. the toxic and anti- 

 toxic effects balance. 



