FOOD AND AIR TURNED INTO FLESH AND ENERGY 91 



which secrete mucus to aid the animal 

 substances. Other larger glands, the 

 salivary glands, empty into the mouth, 

 saliva being also necessary for the 

 purpose of swallowing. Behind the 

 mouth come the pharynx and gullet, 

 which together make a tube with 

 muscular walls which perform the 

 movements of swallowing. Both 

 pharynx and gullet are furnished with 

 numerous mucous glands. The gullet 

 leads to the stomach, an enlargement 

 of the alimentary canal acting mainly 

 as a reservoir. Its walls also are 

 filled with small glands secreting 

 gastric juice which makes proteid 

 foods soluble, that is, carries on the 

 proteid digestion. Next to the stom- 

 ach is the small intestine, a very long 

 tube in the first part- of which is ac- 

 complished the digestion of starches 

 and fats. Its walls are lined with 

 numerous glands, and besides these, 

 two very large glands, the pancreas 

 and liver, pour into it large quantities 

 of liquid. The pancreatic juice di- 

 gests the starch and fat and also any 

 left-over proteids. The liver fur- 

 nishes the bile, but its functions being 

 mainly other than digestive, they need 

 not be discussed here. 



The walls of the small intestine fur- 

 nish the principal surface for the absorp- 

 tion of digested food. This surface is 

 greatly increased by millions of small 



in swallowing dry 



^WM 



— z hH^^_J93^^1 



Fig. 55. — Common 

 earthworm dissected 

 to show alimentary 

 canal, a straight and 

 nearly simple tube 

 through the middle. 

 (Natural size ; after 

 Jordan and Kellogg.) 



projections called 



