2fc THE FUNCTIONS OF ANIMALS. 



said to have slight power of converting starch into sugar; by its 

 alkalinity it helps the action of the trypsin of the pancreas (which, 

 unlike pepsin, acts in an alkaline fluid) ; it affects cell membranes, so 

 that they allow the passage of small drops of fat and oil ; and it is said 

 to have various other qualities. 



(e) In addition to the liver and the pancreas, there are on the walls 

 of the small intestine a great number of small glands, which secrete a 

 juice which seconds the pancreatic juice. The digested material is 

 in part absorbed into the blood, and the mass of food, still being 

 digested, is passed along the small intestine by means of the muscular 

 contraction of the walls known as peristaltic action. It reaches the 

 large intestine, and its reaction is now distinctly acid by reason of 

 the acid fermentation of the contents. The walls of the large intestine 

 contain glands similar to those of the small intestine, and the digestive 

 processes are completed, while absorption of water also goes on ; so 

 that by the time the mass has reached the rectum, it is semi-solid, 

 and is known as fseces. These contain the indigestible and un- 

 digested remnants of the food and the useless products of the chemical 

 digestive processes. 



Absorption. But the food must not only be rendered 

 soluble and diffusible, it must be carried to the different 

 parts of the body, and there incorporated into the hungry 

 cells. It is carried by the blood stream, and in part also 

 by what are called lymph vessels, which contain a clear 

 fluid resembling blood minus red blood corpuscles. 



Absorption begins in the stomach by direct osmosis into the capillaries 

 or fine branches of blood vessels in its walls, and a similar absorption, 

 especially of water, takes place along the whole of the digestive tract. 

 But lining the intestines there are delicate projections called villi ; 

 they contain capillaries belonging to the portal system (blood vessels 

 going to the liver), and small vessels known as lacteals connected 

 with lymph spaces in the wall of the intestine. The lacteals lead into 

 a longitudinal lymph vessel or thoracic duct, which opens into the 

 junction of the left jugular and left subclavian veins at the root of the 

 neck. The contents of the duct in a fasting animal are clear ; after a 

 meal they become milky ; the change is due to the matters discharged 

 into it by the lacteals. It is probable that nearly all the fat of a meal 

 is absorbed from the intestines by the lacteals, but it is not certain in 

 what measure, if at all, this is true of the other dissolved foodstuffs ; 

 the greater part certainly passes into the capillaries of the portal 

 system, which are contained in the villi. The digested proteid, 

 chiefly in the form of amino-acids, passes into the blood of the portal 

 vein, either directly or through the intermediary of leucocytes, which 

 flock to the intestine when proteid food is being digested. 



Function of the liver. We now know the fate of the 

 fats, and of the proteids of the food, and the manner in 



