DIGESTION 367 



waves along the muscular coats. But another kind of movement can be produced 

 by mechanical stimulation, such as that which the presence of food would afford. 

 The nature of this movement was demonstrated by Bayliss and Starling (1899) in 

 the intestine in situ, but separated from any connection with the central nervous 

 system. It can also be obtained in the excised gut, under favourable conditions, 

 and most readily in the colon of the rabbit. A gentle pinch at any spot causes 

 a cessation of the rhythmic contractions in the region just below the place excited, 

 together with a diminution of the state of moderate tonic contraction in which 

 the intestinal muscle normally exists, upon which the rhythmic contractions are 

 superposed. The word, " below," of course, refers to the normal direction of the 

 movement of the contents of the intestine, and would perhaps better be called, 

 "in front of." Coincidently with this relaxation in front of the point excited, 

 there is an increased tonic contraction, with greater vigour of rhythmic move- 

 ments, above, or behind the place excited ; these facts are illustrated by Fig. 95. 

 To this phenomenon, which is common to the alimentary canal from the lower 

 part of the esophagus to the rectum, in a more or less well-marked manner, we 

 gave the name of " The Law of the Intestine." It is clear that it is what would 



FIG. 95. THE LAW OF THE INTESTINE. Contractions of the jejunum 

 traced by a balloon in the lumen. 



At 1, pinched gently about an inch above the balloon. Immediate inhibition of rhythmic 



contractions below, with relaxation of tone. 

 At 2, while still quiescent, a gentle pinch about half an inch below the balloon. After some 



six seconds sudden recovery of tone, with series of strong rhythmic contractions. 

 At 3, similar pinch during normal contractions. Greatly increased strength of contractions. 



(Bayliss and Starling, 1899, Fig. 10.) 



happen if the intestine were distended at any spot by the presence of food, and 

 that it would result in the moving on of the contents. In fact, a lump of cotton 

 wool smeared with soft soap and inserted into the front end of a loop of rabbit's 

 intestine (the colon works best), immersed in warm saline, is gradually passed 

 on and escapes at the lower or posterior end. 



This seems to be a complex act for a muscular mass to perform apart from 

 the central nervous system, but we must remember what there is in the wall of 

 the gut. All along, we have two muscular coats, one arranged in a circular 

 manner, the other in a longitudinal direction ; in some places, as in the stomach, 

 additional layers are provided. Between the two coats there is what may be 

 called a peripheral nervous system, a plexus of nerve cells and fibres, and from 

 this there proceed nerves to the muscular coats. This nerve centre is known as 

 " Auerbach's," or the myenteric, plexus. There is also another plexus, Meissner's, 

 situated between the mucous membrane and the inner, circular, muscular coat. 

 Nerves pass between the two plexuses and to muscles and mucous membrane. 

 The reflex, which we called the "law of the intestine," requires for its manifesta- 

 tion the presence of Auerbach's plexus, but whether Meissner's is also necessary 

 is not known. Nor can it be said whether the afferent impulses for the reflex 

 come from sensory nerve endings in the wall of the gut, or whether the reflex ia 



