72. Observe the experiment that I have tried, in order to ascertain the validity of that fact. Through a wound in the abdomen I drew out a portion of intestine, which I tied at one point. I then returned it, keeping back a part, which I punctured, and introduced into it sufficient atmospheric air to distend all that portion of the bowel between the ligature and the orifice. I then confined the air by another ligature, and reduced the whole. At the end of an hour the animal was opened. I compared the blood of the mesenteric veins, which arise from that portion of intestine distended by air, with the blood of the other mesenteric veins arising from the remainder of the canal: no difference of colour could be observed: the internal surface of the inflated intestine did not exhibit a brighter red. I expected to obtain a more marked effect by repeating the same experiment on another animal with oxygen gas, but I did not perceive any variation in the colour of the blood. As on the mucous membranes, which are ordinarily in contact with the air, this fluid is constantly renewed, and is agitated by a perpetual movement, I tried to produce the same effect in the intestines; for which purpose I made two openings into the abdomen, through each of which I drew a portion of the intestinal tube. I opened these two portions, adapting to one the tube of a bladder filled with oxygen gas, and to the other that of an empty bladder. I then pressed the full bladder so as to make the oxygen gas pass into the empty one through the intermediate portion of intestine which was in the abdomen, so that the warmth there might encourage the circulation. The oxygen gas was in this manner sent many times from one bladder to the other, making a current through the intestine, which from its contraction was more difficult than it at first appeared to be. The abdomen was then opened, but no difference was found between the venous blood returning from that portion of the intestine, and that which flowed from the other parts of the canal. The superficial situation of the mesenteric veins, which are covered by only a fine transparent lamina of peritoneum, and their volume when the animal is not fat, render these comparisons very easy to be made.