658 METABOLISM 



from the portal vein without serious disturbance to the animal. Indeed, 

 the only way by which the problem has been accurately studied is by 

 comparing the blood of the portal circulation with that of the systemic 

 circulation during the injection of a solution of dextrose into one of the 

 smaller branches of the portal vein. 21 In such experiments it has been 

 found that the percentage of sugar is a little less in the blood of the 

 abdominal vena cava than in that of the portal vein, and is still less in 

 the blood of the systemic veins, such as the femoral — results which justify 

 the conclusion that the barriers responsible for taking out some of the 

 absorbed sugar from the blood exist in the liver and in the muscles. The 

 curve in Fig. 18!) will illustrate to what extent the mechanism operates. 



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£PSO B/t>70 Br SO 



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^^ .•* | /Occ & HC L f /flee ■# HCL. 



-*<F*^ Consta_nfc ii/pct/on of /2%Oextrose Solution, 

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Fig. 189. — Curves showing the percentage of glucose in blood after a constant injection of 

 an IS per cent solution into a mesenteric vein. V.C., vena cava, continuous line; P.O., pan- 

 creaticoduodenal vein, broken line; /. iliac, dotted line. 



It will be observed that, so far as can be judged from changes in the 

 concentration of sugar in the blood, the sugar-retaining power of the 

 liver is about equal to that of the muscles. This result shows that the 

 commonly held view is untenable that the liver is capable of removing from 

 the portal blood all of the sugar that is in excess of that present in sys- 

 temic blood. The muscles must assist extensively in this process. 



One objection which may properly be raised to these observations is 

 that the animals on which they 'were made were under anesthesia, and 

 thai the anesthetic may have had a paralyzing effect on the sugar-retainer 

 power of the liver. In view of this criticism it is important to examine the 

 results obtained on animals thai are not under the influence of anes- 



