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IT has long been known that calcium decreases the permeability of cell membranes and capillary walls. It was therefore of interest to study the influence of calcium on the permeability of the intestine.Magee and Sen [1931] showed that the selective permeability of the surviving intestine for glucose requires the presence of calcium ions in the bathing fluid. When the segments were immersed in Ca-free Tyrode, glucose passed out more slowly than xylose; whereas in the presence of calcium, glucose passed out more quickly than xylose.In 1932 Magee and Sen made experiments on living animals also, and showed that the rate of absorption of glucose was subnormal in rats whose blood calcium had been artificially reduced by parathyroidectomy. Furthermore, they found that the addition of calcium to the glucose solution fed caused animals with low blood calcium to absorb at the normal rate. These results strengthened the view these authors put forward that a certain concentration of calcium is necessary for glucose to be absorbed at the normal rate. They also found that, although 0-32 p.c. CaCl2 stimulated absorption in parathyroidectomized rats, the same concentration depressed absorption in normal rats; while 0-02 p.c. CaCi2 on the other hand increased the rate of absorption in normal rats. They also conducted some experiments on rabbits, and found that the serum calcium could be reduced by 2-4 mg./ 100 c.c. either by parathyroidectomy or feeding on a diet deficient in calcium for 6 weeks. They injected 13-5 p.c. glucose directly into the ligated small intestine, and found that there was no constant difference between the rates of absorption in the animals with normal or with low blood calcium.Further experiments on the influence of calcium on intestinal absorption were made by Gellhorn and Skupa [1933] who perfused a frog's intestine with 3-15 p.c. glucose, and the intestinal blood vessels with Ringer solution, keeping the perfusion rate constant. They varied the composition of the Ringer solution, and found that the absorption of glucose was more rapid when KCI and CaCl, were absent than when they were present in the Ringer solution. The addition of 0-0075 p.c. KCI to K-free Ringer solution increased the rate of absorption, while the addition of 0-001 p.c. CaCi2 to Ca-free Ringer caused a strong decrease. Both these effects were reversible, but the decrease caused by 0-02 p.c. CaCl2 seemed to be irreversible. They noted that these changes were not due to contraction or dilatation of the capillaries, since the pressure necessary to keep the perfusion rate constant remained unaltered throughout the experiment. They therefore concluded that potassium

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