Sodium and Water Transport in the Small Intestine of the Dog

　The transport of sodium chloride and water by the intestine of the dog has been examined in vivo using radioactive sodium（Na²⁴）and deuterium．

　The conclusions are as follows：（1）In the hypertonic solution, the movement of water from blood to the intestine is large in the early stage, but in hypotonic it is small．This fact indicates that the movement of water across the wall of the intestine is strongly influenced by the gradient of the osmotic pressure．

（2）The concentration of sodium of the influx solution is almost constant during the course of experiments, though the values vary in each case．Sodium and water move from blood to the intestine in a parallel manner．

（3）The ratio of Naeff to Naiff was some dependent on the concentration of sodium in the intestine．At the concentration of sodium in the intestine of 135mEq/l, which is slightly less than the concentration of sodium in the blood, the ratio approaches unity．The implication here is that the transport of sodium ion across the intestinal wall cannot be considered to occur merely by passive diffusion, and active transport must be postulated．