VARIATIONS IN OXYGEN TENSION. 



137 



by calculating the volume required with the necessary corrections. 

 The air already present in the chamber is thus diluted with pure 

 oxygen to the required degree. The water levels in and out of 

 the chamber were kept equal by removing water from the large 

 jar " F." The apparatus is only approximately accurate. 



Bulb 



Diagram of apparatus. 



The larvae were introduced and removed by the tube "T" of 

 i mm. bore, which was connected to a Y tube and the rubber bulb 

 " H." By manipulating the rubber bulb and the two pinch cocks 

 on the connections of the Y tube, it was possible to pump the 

 larvae in or out of the small beaker " E." This beaker contained 

 the isotonic NaCl. A similar beaker "D" contained a control 

 culture in sea water at the same oxygen tension as " E." A third 

 beaker not shown in the diagram contained another control cul- 

 ture in isotonic NaCl at atmospheric oxygen tension. 



In the first series of experiments the oxygen tension of the 

 NaCl solution containing the larvae was raised gradually. The 

 larvae were placed in the isotonic NaCl solution in the beaker 

 " E " before the oxygen tension was raised in the chamber. The 

 tension in the chamber was then raised to 320 mm. and the salt 

 solution and control were slowly stirred for two minutes. The 

 oxygen tension of the solution and control must rise slowly 

 towards 320 mm., but how long it is before it reaches that figure 



