Abstract
Plant and animal membranes exhibit selective permeability for chemically related substances. The diffusion of simple carbohydrates through the glomerular membrane of the kidney, through the intestinal wall and through the membrane of monocellular organisms has been the subject of a great number of investigations. In several instances, paradoxical phenomena were observed, e. g., that glucose and fructose are taken up by yeast at the same rate when offered singly, but glucose is preferred from a mixture of the two. Chemical reactions following the entry of the substances into the cell are responsible for this unusual behavior. The sugar absorbed from the intestinal wall is carried away subsequently through the mesenteric circulation and does not undergo chemical changes before reaching the liver. On the other hand, in the yeast cell, where the sugar reacts chemically in the immediate proximity of the membrane, the reaction products of the one substance may influence the diffusion of the other one.
In a series of experiments, Cori 1 and Nagano 2 established the absorption coefficients of various monosaccharides in the intestinal tract of the rat. These coefficients referring to glucose as 100, are 110 for galactose, 43 for fructose, 19 for mannose, etc. But from a mixture of equal parts of galactose and glucose, glucose was preferred at a rate of 100:68. 3
We tried to repeat Cori's experiment using polarimetric analysis. Cori's criticism of acute experiments is justified as to the absolute amounts absorbed because of the influence of narcosis and laparato-my on the rate of absorption and because of the variations of body weight and intestinal surface used. However, as we were interested only in the relative rate of absorption of glucose and galactose, we found it most convenient to use the isolated intestinal loop of the rabbit.
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