FOOD AND DIGESTION 371 



pancreatic juice. Its secretion in relationship to food does 

 not indicate that it plays an active part in digestion. It is 

 formed during intra-uterine life and during fasting, and it 

 is produced many hours after food is taken, when digestive 

 secretions are no longer of use in the alimentary canal. Diges- 

 tion can go on quite well without the presence of bile in the 

 intestine, except that the fats are not so well absorbed. The 

 composition of bile strongly suggests that it is a waste product. 

 The pigment is the result of the decomposition of haemoglobin 

 and the acids are the result of protein disintegration. 



All these facts seem to indicate that bile is the medium by 

 which the waste products of hepatic metabolism are eliminated, 

 just as the waste products of the body generally are eliminated 

 by the kidneys. 



Bacterial Action in the Alimentary Canal 



With the food and saliva numerous micro-organisms of 

 very diverse character are swallowed. It has been suggested 

 that the leucocytes formed in the lymphoid tissue at the back 

 of the mouth and pharynx attack and destroy such organisms, 

 but so far definite proof of this is not forthcoming. When the 

 food is swallowed, the micro-organisms multiply for some 

 time in the warm moist stomach, and certain of them, by split- 

 ting sugars, form lactic and sometimes acetic acid. But when 

 sufficient gastric juice is poured out for the hydrochloric acid 

 to exist free, the growth of micro-organisms is inhibited, and 

 some of them, at least, are killed. Others pass on into the 

 intestine, and, as the acid in the chyme becomes neutralised, 

 the acid-forming organisms begin to grow, and, by splitting the 

 sugars, form lactic or acetic acid, and render the contents of 

 the small intestine slightly acid. Towards the end of the small 

 intestine, and more especially in the large intestine, the alkaline 

 secretions have neutralised these acids, and in the alkaline 

 material so produced the putrefactive organisms begin to 

 nourish and to attack any protein which is not absorbed- 

 splitting it up and forming among other substances a series 

 of aromatic bodies, of which the chief are indol, skatol, and 

 phenol. 



This splitting probably occurs through the liberation of 



