ADVANCED EXPERIMENTAL PHYSIOLOGY 181 



diaphragm for the X-rays, short lengths of intestine can generally 

 be clearly defined and their movements studied. A general forward 

 movement of the shadow as a whole, due to peristalsis, can be 

 recognised. At the same time segmentation is seen to occur. The 

 shadow of a short length of intestine, at first of uniform thickness, 

 becomes constricted in its centre. The constriction increases until 

 the single shadow is more or less completely divided into two. 

 Then each half undergoes a similar division, the two central segments 

 of the four produced by the second division joining together. The 

 new central segment then divides again, the segmentation continuing 

 at the rate of about seven divisions a minute. The process is shown 

 diagrammatic ally in Fig. 170. 



A further examination should be made on the following day as 

 early in the morning as convenient. If possible, the bowels should 



m. 



FIG. 170. Diagram of segmentation in the human small intestine. 



(From Hurst's ' Constipation.') 



not be opened before this examination. The whole of the large 

 intestine is generally visible, and its position should be marked out 

 in the vertical and in the horizontal position. In the horizontal 

 position the transverse colon is approximately on a level with the 

 umbilicus ; in the vertical position it is considerably lower. Both 

 the hepatic and splenic flexures are generally acute, especially in the 

 vertical position, and the two limbs of the flexures may form a 

 single shadow. The effect of straining, as it occurs in defaecation, 

 should be observed : the whole of the colon is greatly depressed, 

 the caecum and ascending colon together forming a rounded shadow. 

 Peristalsis is very rarely seen, unless examinations are made every 

 quarter of a minute after a meal in order to catch the " mass 

 peristalsis," which occurs after meals as a result of the gastrocolic 

 reflex. 



