WORKING OVER THE BODY'S INCOME 137 



lymph. There is left in the intestines chiefly ( i ) the undigested 

 (mostly indigestible) fibrous and cell-wall parts of the plant or 

 animal tissues eaten, and (2) the modified secretions of the 

 various glands that have poured into the food tube along the 

 way. This mass of refuse now passes into the large intestine 

 {k, Fig. 74). 



116. The large intestine. In the large intestine the ferments 

 of the digestive juices may continue to act for some time. 

 Gradually, as the mass proceeds along the canal, it becomes 

 drier as the lining of the intestine continues to absorb fluids 

 (there are no villi in the large intestine). Toward the end the 

 only chemical changes going on are those produced by the mil- 

 lions of bacteria that are present in the intestines of all animals 

 that have intestines. 



The mass of material that has accumulated toward the end of 

 the large intestine is of no further use to the body, and should be 

 removed from time to time (see section 131). Birds, having no 

 large intestines, throw off the refuse about as fast as it passes 

 from the small intestine to the rectum (Fig. 78). Other animals 

 and human infants throw off the refuse automatically. 



WORKING OVER THE BODY'S INCOME 



I. The digestive tube of man 



Mouth (organs related to nutrition) 



Teeth ; salivary glands ; (tongue) 

 Pharynx (seven openings) 



Mouth (Windpipe) (Eustachian tubes, 2) 



(Nostrils, 2) Gullet (esophagus) 

 Gullet Stomach 



Swallowing muscles Gastric glands ; muscles 



Small intestine Large intestine 



Glands ; muscles ; villi Connection with small 



Connection with liver and intestine 



gall bladder (Vermiform appendix) 



Connection with pancreas Rectum 



