FOOD AND ITS UTILISATION iii 



saliva may change starch into maltose ; the gastric juice of 

 the stomach converts proteins into peptones ; the pancreas 

 has three ferments— a diastatic one affecting starch, a try ptic 

 one attacking proteins, and a lipase working on fats. The 

 digested sugars and peptones are gathered up from the 

 stomach and intestine by mesenteric veins, which unite to 

 form the portal system entering the liver. In this great 

 filter the digested food carried by the blood is so treated 

 that surplus materials are kept back, thus extra sugar is 

 retained as glycogen, and poisonous stuffs are sifted out. 

 The hepatic veins lead the blood from the liver into the top 

 of the great inferior vena cava, and thus into the heart and 

 the general circulation. The digested fats are collected 

 from the intestine by the lymphatic vessels, and pass thence 

 indirectly into the venous system. The final steps are the 

 utilisation of the digested food, as already stated, for growth, 

 repair, storage, and direct combustion. 



