102 THE BODY AT WORK 



walls, it is not in much need of help. Very different is the 

 position of the large intestine in this respect. Its calibre is 

 much greater, its wall is sacculated, its contents comparatively 

 firm. If the palm of the hand be placed above the right groin 

 and pressure directed upwards, the csecum coli and ascending 

 colon are emptied. If pressure be directed from the extreme 

 right side just below the ribs, across the middle line to the left 

 side, the transverse colon is emptied. The descending colon 

 needs pressure from above downwards on the left side ; the 

 sigmoid flexure, pressure above the left groin, downwards, and 

 towards the middle line. 



The inner wall of the oesophagus is smooth, save for the 

 wrinkles into which it is thrown when not distended ; but from 

 the cardiac orifice of the stomach onwards the mucous mem- 

 brane of the alimentary canal exhibits folds and other pro- 

 jections which serve many purposes. They serve to delay the 

 food, keeping it longer in contact with the secreting surface. 

 They increase the area pitted with tubular glands ; they increase 

 also the area through which absorption of the products of 

 digestion occurs. On the inner surface of the stomach the 

 folds produce a reticulated pattern. In the upper portion of 

 the small intestine, especially the duodenum, there are promi- 

 nent transverse shelves (valvulse conniventes). No definite folds 

 occur below the upper three-fourths of the small intestine, with 

 the exception of the constrictions of the transverse colon 

 already referred to, which affect the whole thickness of its wall. 

 Throughout the whole of the small intestine the mucous mem- 

 brane projects in finger-like processes, or villi, which give it a 

 characteristic velvety appearance. The villi are longest in the 

 duodenum. 



Lymph-follicles occur at intervals in the intestine. In the 

 ileum they are collected into patches (Peyer's patches), on the 

 side opposite to the line of attachment of the mesentery. They 

 serve both for the supply of phagocytes, which hunt any germs 

 that have penetrated the mucous membrane, and also as 

 stations to which germ-laden phagocytes retreat. 



The wall of the intestine is composed of mucous membrane, 

 submucous tissue, and muscle. The mucous membrane is 

 everywhere pitted with tubular glands, termed in the stomach 

 " gastric glands," and in the intestines, both small and large, 



