228 PHYSIOLOGY OF INDUCED HYPOTHERMIA 



passes through the COo absorber and the circuit is completed by returning the gas 

 to the respirator valve and the base of the "lung." A graduated oxygen burette with 

 leveling bulb is connected to the system. 



Since all parts of the gas system are relatively rigid (except the water level in 

 the oxygen burette and the blood level in the reservoir flask, including the blood- 

 filled tubing leading to the thermometer well) the oxygen consumption is read di- 

 rectly from the graduated burette, after restoring the initial manometric pressure 

 (1 cm. H2O) with leveling bulb. It is essential that the level of blood in the ther- 

 mometer well be at its initial level each time an oxygen reading is made. Since 

 changes in the volume of fluid within this rigid- walled system will be reflected in 

 the oxygen measurements, appropriate corrections must be made for the volume of 

 all samples withdrawn or materials added to the system. Another correction factor 

 is required when the standard alkali bottles are changed. The final volume of oxygen 

 utilized is then corrected to standard temperature and pressure. 



The liver preparation with portal vein and bile cannulae in place is supported on 

 a wire-mesh stage wrapped with cellophane to protect the liver. The stage and liver 

 are enclosed between two glass dessicator lids. This minimizes the loss of CO2 

 diffusing from the liver capsule and hepatic vein outflow, and maintains the liver 

 in an environment of constant humidity. The opening in the upper lid contains a 

 rubber stopper with glass tube connecting the "arterial" flow from the "lung" with 

 the portal vein cannula, while the opening in the lower lid has a standard taper 

 joint fitted to the thermometer well. The bile cannula is placed through a small 

 opening drilled in the lower lid and a graduated tube attached to collect bile. 



Methods. A non-fasting rabbit of either sex is anesthetized with pentobarbital 

 (30 mg./Kg.) and heparinized. The common bile duct and portal vein are can- 

 nulated. The liver with attached cannulae is rapidly excised, weighed, and placed 

 in the perfusion apparatus. The liver is without circulation for an interval of 5 to 

 10 minutes. The perfusate used is heparinized whole rabbit blood drawn from 

 donor rabbits by cardiac puncture. The pooled donor blood (300 ml.) is diluted 

 with normal saline (150 ml.) and a commercial 5 per cent protein hydrolysate solu- 

 tion in 5 per cent glucose (50 ml.). The final hematocrit is 20. Aureomycin, 25 mg., 

 is added to the perfusate. The gas system is flushed with oxygen several times, and 

 an equilibration period of 10 to 30 minutes allowed for the gas mixture, perfusate, 

 and liver before starting measured observations. 



Oxygen uptake was determined volumetrically using the method described above. 

 Carbon dioxide production was determined by titration of the standard alkali 

 solution. 



When the conjugation of morphine or thiopental was to be studied, 50 mg. of the 

 drug were added to the reservoir flask and hepatic vein samples analyzed for free 

 and bound morphine. 



When the effect of temperature was to be studied, the temperature of the blood 

 and cabinet for the first 90 minutes was 24° C. ; then the cabinet heater was started 

 and the temperature raised to 37° C. for two hours, a second dose of 50 mg. 

 morphine was added to the reservoir and hepatic vein samples analyzed. 



Free and bound morphine present was determined l)y the ultraviolet spectro- 

 photometric method of Goldbaum.^ 



