DIGESTION AND FOOD. 21 



tractile power, and when it draws itself down, it diminishes 

 the capacity of the stomach so as to press upon its contents, 

 however small they may be; and again, it expands so as to 

 allow the sack to be enlarged for the reception of whatever 

 food or liquid is then thrown into it. 



29. The inner or mucous coat (Fig. VI. a) covers the inner 

 surface of the organ. It is loose, soft, spongy, and porous. 

 It is not elastic, and does not stretch and contract, when the 

 stomach is enlarged or diminished. But when the organ is 

 distended, this membrane is smooth; and when contracted, it 

 is drawn into folds, like the skin of the palm of the hand, 

 or of the inner side of the joints of the fingers when closed, 

 or of the outside when open. 



30. The anatomy of these three coats is somewhat familiar 

 to most people who have eaten tripe, vvhiclj is a preparation 

 of the stomach of the ox or cow. The outer layer of this 

 is a dense, tough covering of fatty matter, and comparatively 

 strong. The next or middle layer is composed of reddish 

 fibres. These are stringy, and are what is commonly called 

 the lean meat. This layer differs in thickness in different 

 parts of the stomach. The inner layer is a thick, soft, fatty 

 matter, and filled with superficial cells. The human stom- 

 ach has similar coats, which are arranged in the same man- 

 ner, and perform the same duties. 



31. These three coats, or coverings, constitute the stomach. 

 They have each a distinct part to perform in the digestive 

 process, and each one is fitted for its peculiar work, and for no 

 other. The outer coat gives strength and support to the 

 whole. The middle coat expands and contracts, to give due 

 size to the sack; it produces the motions in the stomach, 

 which agitate the food and promote the work of digestion ; 

 and finally this coat presses the sack down upon the contents, 

 to expel them when they are digested. The inner or lining 

 coat exudes upon its own surface a slimy, mucous substance, 

 which protects it from the irritation of the matters that are 

 put into the organ, and also prepares the gastric juice a 

 powerful fluid which dissolves the food. 



