THE INTESTINES AND INTESTINAL DIGESTION 109 



A simple experiment will enable us to understand the meaning of the term 

 emulsifies. Pour into a glass vessel about an ounce of water, and then a little 

 oil or melted fat (if the latter, the water should be hot). The two liquids 

 remain quite distinct, the oil or fat floating on the water. Now shake the 

 mixture vigorously, and the oil or fat is separated into globules which are dis- 

 tributed throughout the water ; but, on allowing the mixture to rest for a 

 short time, the liquids separate again. Hence we say that oil is insoluble in 

 water. Next, add a little alkali (potash or soda) to the mixture and shake it 

 again. At once a milky fluid is formed, which is termed an emulsion. The 

 fat or oil has been separated by the alkali into extremely minute particles 

 which remain diffused throughout the liquid. 



The bile is a yellow or greenish-yellow fluid, also slightly alka- 

 line, having the following composition : 



Water 859-2 parts 



(Bilin . . . , . 91-5 



Fat ....... 9-2 

 Cholesterin 2-6 

 Mucus and colouring matter . . 29-8 

 Salts ...... 77 



1000-0 



The bile is secreted continuously, at the rate of from thirty to 

 forty ounces daily. If not needed at 

 once for digestion, it passes into the 

 gall-bladder, where it is stored until 

 required. If digestion is going on, it 

 passes direct from the liver, where it is 

 secreted, to the duodenum. 



The chief uses of the bile as a 

 digestive fluid are (i) to assist in emul- 

 sifying fats, (2) to moisten the mucous 

 membrane of the intestine, and (3) to 

 act as a natural purgative by assisting 

 the muscular motions and the secretion 

 of the intestines. 



When the chyme passes into the 

 small intestine, it is soon mingled with 

 the pancreatic fluid, the bile, and the 

 secretions of the intestinal glands ; and 

 these fluids, together with the saliva 

 and the gastric fluid which form part 

 of the chyme, complete the process of 

 digestion. All kinds of foods are now 

 being dissolved, and by the worm-like 

 motions kept up by the muscular fibres 

 of the intestines, the whole is urged 

 slowly on. The dissolved portions are 

 rapidly absorbed by the mucous me.m- 



Fig. 105. The Ileo-caecal 

 Valve. 



and colon ; e and./, loose folds of 

 the mucous membrane, forming 

 the ileo-caecal valve ;g, vermiform 

 appendage- 



