The A.B.-Z. of our own nutrition

by Horace Fletcher

When the food has been distributed through the intestine so as to present the appearance shown in Figure 1, a noticeable feature in most or all of the loops is the total absence of movement. If the animal remains quiet, however, only a few moments elapse before peculiar motions appear in one or another of the loops, or perhaps in several, and last for some time. These motions consist in a sudden division of one of the long, narrow masses of food into many little segments of nearly equal size; then these segments are again suddenly divided and the neighbouring halves unite to make new segments, and so on, in a manner to be more fully described. I have called this process the rhythmic segmentation of the intestinal contents. Further observation reveals peristalsis here and there, and under certain circumstances the typical swaying movements may be seen. All these phenomena are now to be considered in detail.

Figure 1.—Appearance of food in the intestines 5¾ hours after eating. This and other radiographs reduced two-thirds.

Rhythmic segmentation of the intestinal contents.—This is by far the most common and the most interesting mechanical process to be seen in the small intestine. The nature of the process may best be understood by referring to the diagram in Figure 2. A string-like mass of food is seen lying quietly in one of the intestinal loops (line 1, Fig. 2). Suddenly an undefined activity appears in the mass, and a moment later constrictions at regular intervals along its length cut it into little ovoid pieces. The solid string is thus quickly transformed, by a simultaneous sectioning, into a series of uniform segments. A moment later each of these segments is divided into two particles, and immediately after the division neighbouring particles (as a and b, line 2, Fig. 2) rush together, often with the rapidity of flying shuttles, and merge to form new segments (as c, line 3, Fig. 2). The next moment these new segments are divided, and neighbouring particles unite to make a third series, and so on. At the time of the second segmentation (line 3, Fig. 2) the end particles are left small. Observation shows that these small pieces are not redivided. The end piece at A simply varies in size with each division; at one moment it is left small, at the next moment it is full size from the addition of a part of the nearest segment, and a moment later is the small bit left after another division. The end piece at B (probably the rear of the mass) shoots away when the end mass is divided, and is swept back at each reunion to make the large end mass again, only to be shot away and swept onward with each recurrence of the constrictions. Thus the process of repeated segmentation continues, with the little particles flitting towards each other and the larger segments shifting to and fro, commonly for more than half an hour without cessation. From the beginning to the end of a period of segmentation the food is seen to have changed its position in the abdomen to only a slight extent; whether this change is a passing of the food along the loop, or a movement of the loop itself, it is impossible to tell from the shadows on the screen. The change of position, however, is much less conspicuous than the lively division and redivision which the mass suffers so many times from the busy, shifting constrictions.

Figure 2.—Diagram representing the process of rhythmic segmentation. Lines 1, 2, 3, 4 indicate the sequence of appearances in the loop. The dotted lines mark the regions of division. The arrows show the relation of the particles to the segments they subsequently form.

From this typical form of rhythmic segmentation there are several variations. Sometimes, and especially when the mass of food is thick, the constrictions do not make complete divisions and are so far apart that the intermediate portions are relatively large. Moreover, the constrictions do not take place in the middle of each portion, but near one end; thus each portion is constricted, not into halves, but into thirds. If a little pointer is placed at the middle of a segment, when the segments are completely divided into halves, in a few seconds the pointer will be in the middle of the clear space between two segments; but in a few seconds more the first phase will return and the pointer will again be indicating a segment,—two operations intervene between similar phases. When, however, the portions are constricted into thirds, the indicator shows it, since three operations intervene between similar phases. The manner of these changes is made clearer by reference to the diagram in Figure 3. That each portion is constricted into three pieces is proved also by watching the gradual reduction of the portion at the left end of line 1 through lines 2 and 3, and also in the gradual formation of a full-sized portion at the right end of lines 2, 3, and 4. When food undergoing this process is watched, it appears to be affected by a series of constrictions, each of which starts at one end of the mass and marches through to the other end, leaving its impress at short intervals along the length. The progression of the dotted lines from right to left in a, b, c, and d, etc., Fig. 3, gives a notion of these advancing constrictions.

Another variation of the segmentation is shown in Figure 4. In this type there are evidently divisions and subdivisions, i.e., one more operation between the appearance and the reappearance of the same phase than is present in the simple division of the small segments in a long string of food (Fig. 2). This form of segmentation is fairly typical for the constrictions seen in food advancing through the intestine. Sometimes the divisions occur in the middle of a long string of food and leave the ends wholly unaffected.

Figure 3.—Diagram showing the relations of the portions when they are constricted into three pieces. The dotted lines indicate regions of constriction; the arrows indicate the relationship of the pieces to the portions they subsequently form.