558 THE MECHANICAL PROCESSES OF DIGESTION [CH. XXXVII. 



Our knowledge of the intestinal movements rests, first, on 

 observations made on the exposed intestines when the abdomen is 

 opened; secondly, they may be studied under more artificial 

 conditions by taking a length of intestine from a freshly killed 

 animal and placing it in a warm bath of oxygenated Kinger's 

 solution; and thirdly, the most valuable method of all is to study 

 the movements in the intact animal by the X-ray method, as in the 

 work of Cannon and of Hertz. 



Ludwig was the first to call attention to the fact that peristaltic 

 waves are not the only sort of movements which occur. There is in 

 addition what he termed pendulum or swaying movements. In the 

 exposed intestine the propagation of the peristaltic wave is slow 

 but variable; it may be as small as 1 cm. per minute. In man, 

 as shown by X-ray work, it is more rapid, averaging about an inch 

 per minute. The pendulum movements consist of slight waves of 

 contraction affecting both muscular coats, and these are rapidly 

 propagated at the rate of 2 to 5 cms. per second. They cause a 

 movement of the intestine from side to side, and occur at regular 

 intervals of five or six seconds. They are not efficacious in moving 

 the contents onwards, but they bring about a mixing of the contents 

 very thoroughly. 



Cannon observed by the X-ray method in dogs and cats that 

 these pendulum movements produce what he calls " segmentation." 

 A dark shadow, due to the bismuth in the food administered, is at 

 one moment of a certain length like a short sausage; it then 

 constricts in the centre, and divides into two; each half divides 

 again ; then the two central segments join together, and this repeats 

 itself every few seconds. In man, where the same phenomenon can 

 be seen, Hertz timed the rate, and found it occurred about ten times 

 in a minute and a half. This frequent division and subdivision not 

 only ensures admixture with the juices, but brings every portion in 

 turn in contact with the absorbing mucous membrane, and favours 

 the flow of chyle and blood in their respective vessels. 



After a bismuth meal, the shadow appears in the caecum three 

 and a half to five hours after the food is taken. The average time is 

 four and a half hours. Assuming that it begins to leave the stomach 

 half an hour after a meal, the total journey along the small intestine 

 in man occupies about four hours; the small intestine is 22 J feet 

 long, so the rate works out at about an inch (a little more than 

 2 cms.) per minute. 



Nervous Mechanism. The small intestine, like the stomach, has a 

 double nerve supply. 



(1) The Vagus.^ As in the case of the stomach, these fibres are 

 accelerator, and stimulation induces peristaltic movements. If the 

 intestine is contracting peristaltically before the stimulus is applied, 



