CH. XXXV.] MOVEMENTS OF THE INTESTINES 533 



In the case of the large intestine there is no supply from the vagus. 

 The inferior mesenteric nerves are inhibitory in function, and the 

 pelvic nerves take the place of the vagal fibres as excitatory : this 

 refers to both coats of the muscular wall. If one pinches any parti- 

 cular spot, the upward wave of contraction is not so marked as in 

 the small intestine, but the downward travelling wave of inhibition 

 is well seen. 



Duration of Intestinal Digestion. The time occupied by the 

 journey of a given portion of food from the stomach to the anus, 

 varies considerably even in health, and on this account probably it is 

 that such different opinions have been expressed in regard to the 

 subject. About twelve hours are occupied by the journey of an 

 ordinary meal through the small intestine, and twenty-four to thirty- 

 six hours by the passage through the large bowel. 



Drugs given for relief of diarrhosa or constipation act in various 

 ways : some influence the amount of secretion and thus increase or 

 diminish the fluidity of the intestinal contents; others acting on the 

 muscular tissue or its nerves increase or dimmish peristalsis. 



The description just given of the intestinal movements relates to the principal 

 movement observable, and which is of a peristaltic character. The rate of propa- 

 gation of the peristaltic wave is slow but variable ; it may be as small as 1 centi- 

 metre per minute. 



Starling in his recent work on the subject has called attention to another kind of 

 movement which he terms swaying or pendulum movement. These movements, and 

 also the true peristaltic waves, may be seen in the small intestine in a warm saline bath 

 even after all the nerves connecting them to the central nervous system have been 

 cut through ; the pendulum movements consist of slight waves of contraction affect- 

 ing both muscular coats, and these are rapidly propagated at the rate of 2 to 5 centi- 

 metres per second. They cause a movement of the intestines from side to side, and 

 occur at regular intervals of 5 or 6 seconds Their use appears to bring about a 

 mixing of the intestinal contents ; they are not able to move the contents onwards. 



Th^y differ from the true peristaltic waves in being myogenic ; that is, they are 

 due to the rhythmicality of the muscular fibres themselves, and are propagated from 

 one muscular fibre to another. They are not abolished by painting the intestine 

 with cocaine, or by an injection of nicotine. The true peristaltic waves cease under 

 these circumstances, and they are, therefore, co-ordinated reflex actions, but as they 

 continue after all nerves connecting the intestines to the central nervous system are 

 severed, they must be carried out by the local nervous mechanism. This is the only 

 example known of a true reflex action dependent on peripheral nervous structures. 



Intestinal Oncometer. To study the volume changes of vascular origin, a 

 loop of intestine is enclosed in an oncometer like that described on p. 152 (fig. 179). 

 This is a most valuable application of plethysmography, for the loop gives an 

 accurate record of what is occurring in the splanchnic area. 



Defaecation. The act of the expulsion of faeces is in part due to 

 an increased reflex peristaltic action of the lower part of the large 

 intestine, namely, of the sigmoid flexure and rectum, and in part to 

 the action of the abdominal muscles. In the case of active voluntary 

 efforts, there is usually, first, an inspiration, as in the case of coughing, 

 sneezing, and vomiting ; the glottis is then closed, and the diaphragm 

 fixed. The abdominal muscles are contracted, as in expiration ; but 



