INTRODUCTION 13 



albumoses and peptones, and even coagulates the 

 casein of milk, and a lipase, i.e. an enzyme decom- 

 posing fats — in this special case the fats of the milk 

 are chiefly attacked — into glycerol and fatty acids. 

 On its way through the intestine the food subse- 

 quently comes into contact with the pancreatic juice, 

 containing new enzymes, the trypsin, which decom- 

 poses the albuminous substances still further — 

 namely, to amino-acids — than thepepsin, and further 

 a lipase, decomposing all kinds of fats, and another 

 enzyme, maltase, which decomposes one molecule of 

 maltose into two molecules of ^-glucose, whereby 

 one molecule of water is also taken up. The enteric 

 juice, with which the food later on is mixed, contains 

 the enzymes invertase, lactase, and maltase, which 

 break down the molecules of cane-sugar, milk-sugar, 

 and maltose into hexoses of simpler composition, and 

 a very active proteolytic ferment, erepsin, which 

 decomposes peptones into amino-acids. When the 

 food-stuffs have been decomposed into their simple 

 compounds — amino-acids for the proteids, glycerol 

 and fatty acids for the fats, and hexoses for the 

 starches and sugars — they are taken up by the 

 animal body and, by means of new ferments, partly 

 built up to living substances contained in the 

 different tissues, partly burnt down or otherwise de- 

 composed to give the heat necessary to sustain the 

 temperature of the body or to supply it with energy 

 for doing work. Cellulose, which enters into the 

 food of a great number of animals, is partially 

 rendered useful to these by the aid of micro-organisms 



