THE DIGESTION 2O$ 



the muscular coat. Outside of this is the third coat. It 

 is composed of several layers of involuntary muscular 

 tissue, which, by its contraction, causes the food to move 

 along the canal (Fig. 169). 



363. In the walls of the alimentary canal are numerous 

 blood vessels and lymphatics? Opening on its inner sur- 

 face are mouths of ducts from the various glands of the 

 digestive system. Some of the glands are of considerable 

 size and lie outside of the canal ; others are very minute 

 and are embedded in the walls of the canal ; their secre- 

 tions render the food soluble. 



364. The Real Inside of the Body. When we swallow 

 food or drink, we are accustomed to say that it is in the 

 body, but anatomically and physiologically this is not 

 correct. It is on the outside anatomically, because the 

 mucous membrane is continuous with the skin, which is 

 the external covering. It is on the outside physiologically, 

 because the food must pass through the mucous mem- 

 brane before it can be assimilated by the tissues and 

 become of use to the body. In many kinds of sickness 

 the secretion of the digestive fluids diminishes or ceases 

 altogether, and persons sometimes make a sad mistake in 

 thinking they are giving food to the patient, when the 

 food is only irritating the alimentary canal and ferment- 

 ing or decomposing, and never really getting inside of the 

 body. A lean person often eats a great deal, expecting 

 to get fat, and finds that although he has swallowed the 

 food, the nourishment has never really entered his body. 

 Many a dyspeptic is tortured with the gnawings of hunger 

 yet is continually eating, and is hungry still, because he 

 does not really get the food. 



365. The Mouth. The food is held in the mouth for 

 a short time while it is mixed with the watery alkaline 

 fluid called the saliva, and is ground up fine by the teeth. 

 The partition between the nose and the mouth is formed 



