DIGESTION 133 



36. Absorption. With the preparation of the chyle, the 

 work of digestion is completed; but it has not yet become a 

 part of the v blood, by means of which it is to reach the dif- 

 ferent parts of the body. The process by which Jhe liquefied 

 food passes out of the alimentary canal into the blood is called 

 absorption. This is accomplished in two ways ; first, by the 

 blood-vessels, We have seen how the inner membrane of the 

 stomach is underlaid by a tracery of minute and numerous 

 vessels, and how some portions of the food are by them 

 absorbed. The supply of blood-vessels to the intestines is 

 even greater; particularly to the small intestines, where the 

 work of absorption is most actively carried on. 



37. The absorbing surface of the small intestines, if con- 

 sidered as a plane surface, amounts to not less than half a 

 square yard. Besides, the mucous membrane is formed in 

 folds with an immense number of thread-like prolongations, 

 called villij. which indefinitely multiply its absorbing capacity. 

 These villi give the surface the appearance and smoothness of 

 velvet, and during digestion they dip into the canal, and, by 



(which may be bought of any butcher), by means of either water or 

 glycerin. Mince the pancreas finely and add sufficient of either of these 

 liquids to cover it, set aside for a day and strain or filter. The glycerin 

 extract will keep for a long time ; the watery extract soon spoils. 



The pancreatic juice has a digestive action on all the food-stuffs. 



Its action upon boiled starch may be demonstrated by repeating the 

 experiments detailed under "Saliva," only substituting the extract of the 

 pancreas for the saliva. 



Its action upon albuminoids is shown by adding to a few teaspoonfuls 

 of the pancreatic extract some finely minced meat, or a part of the 

 white of a boiled egg. But as the action of the pancreatic juice can only 

 proceed in an alkaline medium, it is necessary to be certain of the 

 alkalinity of the fluid. This is best done by adding about five grains of 

 carbonate of soda (washing soda) to each ounce of pancreatic extract. 

 Set the test-tube aside in a warm place for a few hours, when the meat 

 or white of egg will be found entirely dissolved. 



Its action upon fats may be shown by shaking up in a test-tube a 

 quantity of the extract with an equal part of melted lard or oil, when \vc 

 will obtain a very perfect emulsion. 



36. How much thus far has been done with the food ? 



37. The next process ? Give the first 



