58 PHYSIOLOGY AND TEMPERANCE. 



CHAPTEE V. 

 DIGESTION. 



1. Need for Food. It has been explained why the body 

 requires daily food : in the first place, to build up the body, 

 and in the second place, to supply material for renewing the 

 tissues, which are constantly wearing out. The arrangement 

 provided for converting the various food stuffs into blood 

 is as perfect in design as we have seen the construction 

 of the body to be. An immense tube, beginning at the 

 mouth, passes through the body. This tube is not of uniform 

 size. In some places it is dilated, while in others it is quite 

 narrow. The gullet, for instance, is a narrow tube, while the 

 stomach is an expansive sac. This alimentary canal, as it is 

 called, is lined by a -thin membrane, a continuation of the 

 skin. It is seen in the lips, where a sharp line marks the 

 boundary between the skin and this reddish mucous mem- 

 brane. Outside the mucous membrane are other layers, which 

 go to form the walls of this canal. The muscular layer, or 

 coat, by involuntary action passes the food along the tube. 

 Numerous blood and lymphatic vessels form a part of the 

 walls. These lymphatics are located in the intestinal tube 

 for absorbing and conveying into the system the nutritious 

 portions of the digested food. We find along this canal also 

 the openings of the ducts of the various glands, which pro- 

 vide important fluids to aid in the process of digestion. The 

 glands themselves are mostly situated in the walls. Some, 

 like the salivary gland, are placed at a distance from it. 



That part of the alimentary canal extending from the lips 

 to the stomach, may be divided into the portions forming the 



