The Functional Divisions of the Large Intestine

T HE portion of the alimentary canal in which the final processes of normal digestion occur, and in which almost all the digested food is absorbed, is the small intestine. At the lower end of this long tube is the large intestine, serving, it is usually taught, as a reservoir to receive, store, and periodically discharge the accumulation of waste. Throughout the small intestine the contents are maintained in a semi-fluid state-a state favourable to the chemical processes which the food there undergoes, and favourable also to ease its movement through the canal. The material delivered to the colon is still semi-fluid, but in the colon the absorption of water from it causes the consistency of the waste to become more dense. This change in density of the colonic contents, however, is not uniformly spread over the total length of the colon. The soft semi-fluid or mushy mass is confined to the cacum, ascending colon, and right third of the transverse colon. The contents of the left two-thirds of the transverse colon, the descending and terminal colons, are, as a rule, as formed in consistency as that which is discharged through the anal canal. This difference in consistency of the colonic contents at once raises doubts in our minds as to the value of the purely anatomical subdivisions of the colon, into ascending, transverse, descending, iliac, and pelvic portions, as two distinct physiological segments are thus seen to be present: a proximal segment with soft, mushy contents, and a distal segment with contents of a firm consistency. 'rhe desirability of giving a functional description to the large intestine was first suggested by Holzkneck (1), when he observed for the first time the movement of an opaque meal along the colon under the fluorescent screen. He stated that in this case a column of faecal matter, corresponding to about one-third of the whole length of the colon, was suddenly displaced into the next empty compartment of similar length. This displacement, he stated further, was preceded by the disappearance of the haustral segmentation, both in the region about to be emptied, and in the next section of the gut. Immediately the latter was filled, the haustral segmentation reappeared. This procedure was repeated about three times during the twenty-four hours. Up until this observation it had been taught that the motion of the faecal contents of the large intestine was that of a …