726 PHYSIOLOGY 



expect to paralyse any local nervous structures in the wall of the gut. 

 Bayliss and Starling concluded that these rhythmic contractions were 

 myogenic,* that they were propagated from muscle fibre to muscle fibre, and 

 that they coursed down the gut at the rate of about 5 cm. per second. Since, 

 however, they may apparently arise at any portion of the gut which is subject 

 to any special tension, it is not easy to be certain that a contraction recorded 

 at any point is really propagated from a point two or three inches higher up. 

 These contractions must cause a thorough mixing of the contents of the gut 

 with the digestive fluids. On examining under the Rontgen rays the 

 intestines of a cat which has taken a large meal of bread and milk mixed with 

 bismuth some hours previously, a length of gut may be seen in which the 

 food contents form a continuous column. Suddenly movements occur in this 



Fro. 343. Diagram of the 'segmentation' (pendular) movements of the intestines as 

 observed by the Rontgen rays, after administration of bismuth. (CANNON.) 



1. A continuous column, intestinal movements being absent. 2. The column 

 broken up into segments. 3. Five seconds later, each segment divided into two, 

 the halves joining the corresponding halves of adjacent segments. 4. Condition 

 (2) repeated five seconds later. 



column, which is split into a number of equal segments. Within a few 

 seconds each of these segments is halved, the corresponding halves of ad- 

 jacent segments uniting. Again contractions recur in the original positions, 

 dividing the newly formed segments of contents and re-forming the segments 

 in the same position as they had at first (Fig. 343). ^If the contraction is a 

 continuous propagated wave, it is evidently reinforced at regular intervals 

 down the gut, so as to divide the column of food into a number of spherical 

 or oval segments. The points of greatest tension immediately become the 

 points which are midway between the spots where the first contractions 

 were most pronounced. The second contractions therefore start at these 

 points of greatest tension, and divide the first formed segments into two parts, 

 which join with the corresponding halves of the neighbouring segments. In 

 this way every particle of food is brought successively into intimate contact 



* Magnus has shown that strips of the longitudinal coat, pulled off^from the small 

 intestine of the cat, may continue to beat regularly in oxygenated Ringer's solution. He 

 stated that these contractions only occurred if portions of Auerbach's plexus were still 

 adherent to the muscle fibres, and concluded therefore that the rhythmic, like the 

 peristaltic, contractions, were neurogenic. Gunn and Underbill however have obtained 

 well-marked rhythmic contractions from strips of muscle entirely free from any remains 

 of the nerve plexus, thus confirming the view enunciated above. 



