26 Animal Life and Intelligence. 



the milk. Now, of all the materials thus consumed, only 

 the water, salts, and sugar are capable, in their unaltered 

 condition, of passing through the lining membrane of the 

 alimentary canal, and thus of entering the body. The 

 albuminous materials, the starchy matter, and the fat — 

 that is to say, the main elements of the food — are, in their 

 raw state, absolutely useless for nutritive purposes. 



The preparation of the food begins in the mouth. The 

 saliva here acts upon some of the starchy matter, and 

 converts it into a kind of sugar, which can pass through 

 the lining membrane of the alimentary canal, and thus 

 enter the body. The fats and albuminous matters here 

 remain unaltered, though they are torn to pieces by the 

 mastication effected by the teeth. In the stomach the 

 albuminous constituents of the meat are attacked by 

 the gastric juice and converted into peptones ; and in this 

 new condition they, too, can soak through the lining 

 membrane of the alimentary canal, and thus can enter the 

 body. In the stomach all action on starch is arrested; 

 but in the intestine, through the effect of a ferment 

 contained in the pancreatic juice, this action is resumed, 

 and the rest of the starch is converted into absorbable 

 sugar. Another principle contained in pancreatic juice 

 takes effect on the albuminous matters, and converts them 

 into absorbable peptones. The pancreatic juice also acts 

 on the fats, converting them into an emulsion, that is to 

 say, causing them to break up into exceedingly minute 

 globules, like the butter globules in milk. It furthermore 

 contains a ferment which splits up the fats into fatty acids 

 and glycerine ; and these fatty acids, with an alkaline 

 carbonate contained in small quantities in pancreatic juice, 

 form soluble soaps, which further aid in emulsifying fats. 

 The bile also aids in emulsifying fats. 



The effect, then, of the various digestive fluids upon 

 the food is to convert the starch, albuminous material, 

 and fat into sugar, peptones, glycerine, and soap, and thus 

 render them capable of passing through the lining mem- 

 brane of the canal into the body. 



