478 THE HUMAN BODY 



part of the emergency reaction of the Body, therefore, consists in 

 suspension of activity in these organs. This has been noted pre- 

 viously (p. 196). 



Movements of the Large Intestine. During the passage of the 

 food through the small intestine the greater part of its nutritive 

 content is absorbed, but practically none of the water, so that it 

 is delivered through the ileocolic valve to the large intestine in a 

 very watery condition. The parts of the large intestine next to 

 the small intestine, the ascending and transverse colon, show an 

 interesting movement in the form of an antiperistalsis. This is a 

 peristaltic wave which begins in the transverse colon and sweeps 

 toward the ileocolic valve. It would tend to force the material 

 within the colon back into the small intestine did not the ileocolic 

 valve prevent. The result of this movement is a churning and 

 mixing of the contents whereby the absorption of the last useful 

 materials, including the water, is promoted. As the large in- 

 testine is filled more and more from the small, some of its contents 

 are crowded, in spite of the antiperistalsis, into the descending 

 colon, where regular peristaltic waves carry them on to the sigmoid 

 flexure and the rectum, whence they are discharged from the Body. 

 There is evidence that the stimulus for these intestinal waves is 

 mechanical, depending on stretching of the walls by the intes- 

 tinal contents. 



Importance of Roughage. As the result of the absorption of 

 water from the contents of the large intestine the material re- 

 maining, which consists of undigested substances, bacteria, the 

 products of bacterial action, and some waste products excreted in 

 the bile (p. 518), tends to become dry and closely packed. If the 

 diet is poor in roughage (p. 429) so little room is occupied by this 

 material that the necessary mechanical stimulation fails to be 

 forthcoming for the movements by which it should be carried along 

 to the region of discharge. There is, therefore, stagnation in the 

 large intestine, and this, by permitting time for a more complete 

 absorption of water, makes the condition of affairs still worse, and 

 the evacuation of the colon still more difficult. The inclusion of 

 considerable roughage in the diet (bran, the pulp of vegetables 

 and fruits, particularly apples, popcorn) by increasing the bulk 

 of the intestinal contents favors the onward movement of the 

 material, and tends against stagnation. We need to remember 



