168 MEASUREMENT OF OXYGEN CONSUMPTION 



one end and fitting to the other a piece of rubber tubing which can be 

 clamped shut. Various dilutions of the blood are made (with a satu- 

 rated solution of ether in sea water), each of which is placed in a 

 separate tube. In one tube undiluted blood is placed. All the tubes 

 are clamped shut to prevent the evaporation of ether. 



The ether prevents the decolorization of the blood and the various 

 dilutions furnish shades of color which serve as standards in subse- 

 quent experimentation. 



If fresh water organisms are used in the experiments the procedure 

 must be modified. Since the salt content of the blood is approximately 

 that of sea water it must be reduced by dilution or by dialysis. If this 

 is carried beyond a certain point precipitation occurs and the color 

 of the aerated blood is paler in consequence. 



The organisms are placed in glass tubes, provided with rubber 

 tubing as described above, and blood (diluted or undiluted) is added; 

 the tubes are then clamped shut, taking care to exclude bubbles of 

 air. The observer then notes the time required to produce a definite 

 change^ in color (as determined by comparison with the tubes con- 

 taining blood to which ether has been added). ^ It is desirable to ob- 

 serve the tubes against a dark background, preferably while facing 

 the source of light. The best results are usually obtained by viewing 

 the tubes from the end. For this purpose the tubes are inverted so 

 that the rubber tubing is below; the organisms sink into it and the 

 rubber tubing may be temporarily pinched off above the organisms 

 so they cannot be seen. 



As soon as a definite change in color is observed the tubes con- 

 taining the organisms may be opened and shaken with air so as to 

 restore the original color. There must be a control tube containing 

 blood without organisms or ether; if this control becomes decolorized 

 the experiment must be rejected, unless the decolorization is so slow 

 as not to interfere with the result. Freshly drawn blood does not 

 decolorize except very slowly; this is also true of freshly dialyzed 

 blood, and of blood heated'' for 5 minutes to 60°C. Blood preserved 



^ The tubes should be shaken from time to time. 

 * A "Daylight" lamp was used in most of the experiments. 

 ^Heating at lower temperatures (40-55°C.) for a longer time may be pref- 

 erable. 



