74 INTRODUCTION TO GENERAL PHYSIOLO(,Y 



enzyme that accelerates the hydrolysis and synthesis of esters. 

 This enzyme is known as " lipase" 



It is not found in any appreciable quantity in the saliva or in 

 the gastric juice. The first change that takes place is when the 

 pancreatic juice is met with. This contains a powerful lipase, and 

 effects the hydrolysis of fats into glycerol and the particular fatty 

 acid. These higher fatty acids are insoluble in water, but are 

 dissolved by the bile. This liquid is a secretion made by the liver, 

 and poured into the intestine by a duct close to that of the 

 pancreas. Bile contains salts of two related complex acids, which 

 have a great effect in lowering surface tension. From what has 

 been said in the previous chapter in regard to the effect of lowering 

 surface tension in increasing the dispersion of colloids, we shall not 

 be surprised to find that the activity of lipase is increased in a 

 marked degree by the presence of bile. Indeed, some kinds of 

 lipase appear to be practically inert in its absence. The increase in 

 activity is, no doubt, due to the increase in the surface of the 

 enzyme, owing to its greater dispersion ; but it may also cause a 

 greater dispersion of the fat itself. 



Fatty acids and glycerol are absorbed together and, somewhat 

 remarkably, at once recombined in the wall of the intestine to 

 the original neutral fats, which can be seen in the cells of the 

 intestinal surface (E., p. 195). Although the actual proof is difficult, 

 there can be little doubt that this synthesis is effected by lipase, 

 acting in a system in which the water has been reduced by some 

 means. 



The fine globules of fat which then pass out of the cells do not 

 enter the blood at once, but are taken into a space which is in 

 connection with a system of branching vessels, called lymphatics. 

 These have their origin in the spaces of the tissues of all kinds of 

 organs, and finally unite in a large vessel which enters the veins at 

 the root of the neck. The fat thus enters the Dlood in very fine 

 globules, and can be detected there after a meal containing fat. 



What fat is not required for current use as a source of energy is 

 stored up in subcutaneous and other connective tissue in numerous 

 parts of the body. This is the special advantage it possesses over 

 other kinds of food, since the capacity of storage is practically 

 unlimited. 



Like carbohydrate, there are intermediate products formed 

 before fat is completely oxidised to carbon dioxide and water. The 

 process is not completely understood, and involves more chemical 

 details than can be given here. 



