312 MOVEMENTS OF THE INTESTINE. 



pharyngeal nerve), stomach, and further, by stimulation of the uterus 

 (pregnancy), intestine (inflammation of the abdomen), urinary apparatus 

 (passing a renal calculus), and also by direct stimulation of the vomiting 

 centre. 



Vomiting produced by the thought of something disagreeable appears to be 

 caused by the conduction of the excitement from the cerebrum to the Vomiting 

 centre. Vomiting is very common in diseases of the brain. Section of both vagi 

 prevents vomiting. 



Emetics act (1) partly by mechanically or chemically stimulating the ends of 

 the centripetal (afferent) nerves of the mucous membrane. Tickling the fauces, 

 touching the surface of the exposed stomach (dog); and many chemical emetics 

 e.g., cupric and zinc sulphate and other metallic salts act in this way. (2) Other 

 substances cause vomiting when they are introduced into the blood (without being 

 first introduced into the stomach), and act directly upon the vomiting centre, e.g., 

 apomorphin. (3) Lastly, there are some substances which act in both ways, 

 e.g., tartar emetic. Emetics may also remove mucus from the lungs, and in this 

 ease it is probable that the emetic acts upon the respiratory centre, and so favours 

 the respirations. [According to Lauder Brunton, cupric sulphate acts even when 

 injected into the blood.] 



Vomiting is analogous to the process of rumination in animals that chew the 

 cud. Some persons can empty their stomach in this way. 



159. Movements of the Intestine. 



Peristalsis. The best example of peristaltic movements is afforded 

 by the small intestine ; the progressive narrowing of the tube pro- 

 ceeds from above downwards, thus propelling the contents before it. 

 Frequently after death, or when air acts freely upon the gut, we may 

 observe that the peristalsis develops at various parts of the intestine 

 simultaneously, whereby the loops of intestine present the appearance 

 of a heap of worms creeping amongst each other. The advance of new 

 intestinal contents again increases the movement. In the large 

 intestine, the movements are more sluggish and less extensive. The 

 peristaltic movements may be seen and felt when the abdominal walls 

 are very thin, and also in hernial sacs. They are more lively in vegetable 

 feeders than in carnivora. The peristalsis is perhaps conducted directly 

 through the muscular substance itself (as in the heart and ureter 

 Engelmann). 



Method of Observation. Open the abdomen of an animal under a'6 p.c. saline 

 solution to prevent the exposure of the gut to air (Sanders, and Braam-Houckgeest). 



The ileo-colic valve (Bauhin's valve, 1579, known to Rondelet in 

 1554), as a rule, prevents the contents of the large intestine from pass- 

 ing backwards into the small intestine. The movements of the 

 stomach and intestine cease during sleep (Busch). 



However, when fluid is slowly introduced into the rectum through a tube, it 

 may pass upwards into the intestine, and even go through the ileo-colic valve into 

 the small intestine. 



