ABSORPTION. 23 



neutral 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. ^ 



(«) 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 jiiice 

 which probably seconds the pancreatic juice^ The digested materiaFls 

 in part absorbed iiTfcTnie blood.'aridtTTe 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 conteiTts. The walls of tlT?Ktge"intestine contain glands similar 

 to thosiTortTie small intestine, and the digestive processes are completed, 

 while absorption also goes on ; so that by the time the mass has reached 

 the rectuin, it is semi-solid, and is known as freces. These contain all 

 the indigestible ancT'unTli^ested reriinanfsT)f"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 ??ii?ms 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 special hair-like 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 food stuff's ; the greater part 

 certainly passes into the capillaries of the portal system, which are con- 

 tained in each villus. The peptone or digested proteid, as it passes 

 through the cells of the villi, is changed into other proteids nearly 

 related to those of the blood, for no peptone is found in the portal vein. 



Function of the Liver. 



We now know the fate of the fats, and of the proteids 

 of the food, and the manner in which they p)ass into the 

 blood ; but we must follow the starchy material, or carbo- 



