Peritoneum
Collier's New Encyclopedia (1921)
one of the most difficult parts in the human anatomy for a teacher to explain intelligibly to his pupils, and the last that the student is able thoroughly to understand. From birth till death, the bowels are constantly moving and gliding over each other, in a worm-like perpetual motion, called peristaltic motion. It will be self-evident that this day and night friction of such delicate textures as those composing the integuments would, in the 70 years of man's life, wear out, or at least in time most seriously injure them. To prevent this friction, nature has provided the peritoneum, an immense shut-bag. The inside that portion out of sight-presents, when cut open, a smooth, glairy surface, studded with innumerable vessels, always pouring out a thin, in, smooth fluid, like the liquid white of an egg, allowing the two sides, when rubbed together, to glide over each other, as if oiled, without check or the slightest friction. The outside of this is rough and granulated. The peculiarity of the inner and outer sides of this immense bag lies in this, that the surface of the first however firmly pressed, can never grow together, or keep long in contact; while that of the other is rough, dry, and adheres firmly to all with which it comes in contact. This external side, then, adheres to the muscles of the abd abdomen, and to every portion of the intestines, but in such a manner that between every convolution, or twist of the bowels, a fold of peritoneum accompanies it, so that betwee between the bowel above or below there is always the two glairy sides rubbing against each other, and allowing the intestines to glide about without let or hindrance, the bowels being always or the outside of the bag, but always glid ing over the two inner sides. The peri toneum is a serous membrane, and, in the same way as it covers the bowels, lines and invests every organ in the abdominal and pelvic cavities.
What Has Changed in the Last Century
The anatomy Collier's described in 1921 — the "immense shut-bag" of serous membrane, slick on its inner face and adherent on its outer — is still taught in much the same terms, though the closed-bag image is qualified today: in women the cavity opens to the outside through the fallopian tubes. What has changed utterly is the clinical standing of the membrane. In 1921 a burst appendix or perforated ulcer meant peritonitis and very often death; sulfa drugs from the later 1930s, penicillin in the 1940s, and modern surgery turned that into a usually survivable emergency. The peritoneum has since become a working tool rather than a passive lining: it serves as the filtering membrane in peritoneal dialysis for kidney failure (routine after the Tenckhoff catheter of 1968), and the cavity is routinely inflated with carbon dioxide for keyhole laparoscopic surgery, a technique unknown to Collier's readers.
Written for this edition, 2026.