_Vomiting_ is more or less the reverse of swallowing and is generally preceded by a feeling of _nausea_, which starts up _retching_, a more or less involuntary effort of the stomach to throw off its contents. To relieve the retching a long breath is taken, followed by a deep expiration that opens the cardiac end of the stomach and allows the abdominal muscles to force the food out. After much vomiting and prolonged retching the pyloric end of the stomach may be affected and bile will then appear in the vomitus. _Artificial vomiting_ may be produced by irritation of the gastric nerve center in the brain or by irritation of the stomach itself. [Illustration: FIG. 54.--The intestinal canal: 1, Stomach; 2, duodenum; 3, jejunum; 4, ileum; 5, cecum; 6, vermiform appendix; 7, ascending colon; 8, transverse colon; 9, descending colon; 10, sigmoid flexure; 11, rectum. (Leidy.)] =Intestinal Canal.=--From the stomach the food passes into the intestinal canal, a convoluted tube which extends from the stomach to the anus and in which, more particularly in the upper portion, the greater part of the digestion and absorption of food takes place. This tube, which is about six times the height of its possessor, consists of two parts, the small and the large intestines, the first four-fifths, or about 25 feet, being small intestine. It occupies the central and lower parts of the abdominal cavity and a small portion of the pelvic cavity, and is attached to the spine by the mesentery, which, however, allows great freedom of motion, so that there is little fixation to the loops of the small intestines. =The Small Intestine.=--The small intestine opens out of the stomach and has three divisions: 1. the _duodenum_, which is only about ten to twelve inches long; 2. the _jejunum_, so called because it is generally empty after death, which is about two-fifths of the remainder and lies chiefly in the umbilical region and the left iliac fossa, and 3. the _ileum_ or _curved intestine_, the remaining three-fifths, which gets its name from its numerous coils and which lies in the middle and the right side of the abdomen. There is no direct division between the jejunum and the ileum, but the first part of the former and the last part of the latter are quite different in character. At its entrance into the large intestine the ileum is guarded by the _ileo-cecal valve_. [Illustration: FIG. 55.--1, Central lacteal; 2, capillary network; 3, columnar cells.]